Baz Luhrmann's epic film Australia has been criticised by many, and most vociferously by Germaine Greer, for sanitising the country's colonial history. At the same time it has served the purpose of making Australia look like a great place to go on holiday - its release was accompanied by reams of coverage in the travel sections of newspapers and a lavish advertising campaign by the Australian tourist board. This kind of marketing is hardly new - throughout cinematic history, films have served political and social ends. But in order to understand the influences at play in Hollywood today it is still worth asking in more detail: what prompted 20th Century Fox to produce this kind of material? The answer becomes clearer when we learn that the studio's parent company is Rupert Murdoch's News Corporation, which worked hand in hand throughout the film's production with the Australian government. The arrangement works well for both parties: the government benefits from the increase in tourism, and in turn Murdoch will receive tens of millions of dollars in tax rebates.

This is just one example of how the content of Hollywood movies is determined not only by the demands of the box office and the vision of studio "creatives", but also by those higher up the economic food chain. Indeed, in its cinema power list the Hollywood Reporter placed ­Rupert Murdoch at number one. Steven Spielberg, at number three, was the only director in the top ten.

The economic structure of the film industry is built around the dominant Hollywood studios ("the majors"), each of which is a subsidiary of a much larger corporation. Each studio is therefore not a separate or independent business, but rather just one of a great many sources of revenue in its parent company's wider financial empire. So, just as 20th Century Fox is owned by News Corp, Paramount is a subsidiary of the media conglomerate Viacom. Universal is owned by General Electric/Vivendi, Disney by the Walt Disney Corporation, and so on. These parent companies are huge corporations, and their economic interests are sometimes closely tied to politicised areas, such as the armaments industry. They also depend on governments, which have the power to regulate in their favour and grant them tax breaks.

This is not to say that the content of a studio's films is determined entirely by the political and economic interests of its parent company; studio CEOs typically have considerable leeway to make the pictures they want to make, without any direct interference. But it is important to understand how and why Hollywood studios are tied into these wider corporate interests. At best, such interests contribute to a culture of conservative film-making. At worst, it is certainly not unknown for parent companies to take a conscious and deliberate interest in ­certain films.

To take one example: in 1969, Haskell Wexler - the cinematographer for One Flew Over the Cuckoo's Nest - had considerable trouble releasing his classic Medium Cool, which riffed on the anti-war protests at the Democrat convention the previous year. According to Wexler, documents he has received under the Freedom of Information Act reveal that on the eve of the film's release, Chicago's mayor and others in the Democratic Party let it be known to Gulf & Western (then the parent company of Paramount) that if Medium Cool was released, certain tax benefits and other perks would be withheld.

In a telephone interview, Wexler told us that Hollywood's business leaders "have no conscience". He explained how this corporate agreement was made discreetly: "Paramount called me and said I needed releases from all the [protesters] in the park, which was impossible to provide. They said if people went to see the movie and left the theatre and did a violent act, then the offices of Paramount could be prosecuted." Although Paramount was obliged to release the film, it successfully pushed for an X ­rating, advertised it feebly, and forbade Wexler from taking it to film festivals. Hardly the way to make a profit on a movie, but certainly the way to protect the broader interests of the parent company.

More recently, the Walt Disney Company tried to withhold Miramax's Fahrenheit 9/11 (2004), the Michael Moore blockbuster. Miramax insisted Disney had no right to block it from releasing the film since its budget was well below the level requiring Disney's approval. Disney representatives responded that they could veto any Miramax film if it appeared that its distribution would be counterproductive to the interests of the company. Ari Emanuel, Moore's agent, alleged that Disney's boss Michael Eisner had told him he wanted to back out of the deal due to concerns about political fallout from conservative politicians, especially regarding tax breaks given to Disney properties, including Walt Disney World in Florida (Florida's governor was the then-president's brother, Jeb Bush). Disney denied any such high political ball game, explaining that they were worried about being "dragged into a highly charged partisan political battle" and alienating customers.

Disney has a strongly conservative tradition: Walt himself was a virulent anti-communist (though some of the more salacious rumours about him being a secret fascist and FBI informer are decidedly speculative). Corporate and government sponsors helped Disney make films promoting President Eisenhower's "Atoms for Peace" policy as well as the infamous Duck and Cover documentary which suggested to schoolchildren that they could survive an atomic attack by hiding under their desks. Even now, a longtime member of Disney's board of directors is John E Bryson, who is also a director of the Boeing Company, one of the world's largest aerospace and defence contractors. Boeing received $16.6bn in Pentagon contracts in 2002, in the ­aftermath of the US invasion of Afghanistan.

Certain Disney films do appear to have been given preferential treatment for political reasons. When Disney released Pearl Harbor - a simplistic mega-budget movie which celebrated the American nationalist resurgence following that "day of infamy"- it received lamentable reviews. Nevertheless, Disney unexpectedly decided in August 2001 to extend the film's nationwide release window from the standard two to four months to seven months, meaning that this "summer" blockbuster would be screening until December. In addition, Disney expanded the number of theatres in which the film was showing from 116 to 1,036.

While such fare finds an easy route into the world's multiplexes, more politically challenging films are left to flounder for funding. Oliver Stone's Salvador (1986) was a graphic exposé of the Salvadorian civil war; its narrative was sympathetic to the leftist guerrillas and explicitly critical of US foreign policy, condemning the United States support of Salvador's right-wing military and infamous death squads. Stone's film was turned down by every major Hollywood studio, and was eventually financed by British and Mexican investors. More recently, controversial counterculture documentaries such as Loose Change, which argued that 9/11 was an "inside job", and Zeitgeist, which presents a frightening picture of global economics, have been viewed by millions through the internet when corporate media wouldn't touch them.

Universal Studios has backed a number of socially and politically critical films including Children of Men, Jarhead, and The Good Shepherd. However, at times it has been evident that the interests of the studio's parent company, General Electric, have played a part in decision-making. GE's most lucrative interests relate to weapons manufacturing, producing crucial components for hi-tech war planes, advanced surveillance technology, and essential hardware for the global oil and gas industries, notably in post-Saddam Iraq. Both GE's former and current CEOs had links to the Bush administration: Jack Welch (CEO from 1981 to 2001) is a declared Republican who announced his disdain for "protocol, diplomacy and regulators" and was even accused by the California congressman Henry Waxman of pressuring his NBC network to declare Bush the winner prematurely in the 2000 "stolen election" when he turned up unannounced in the newsroom during the poll count. Welch's successor, the current CEO Jeff Immelt, is a neoconservative and was a significant financial contributor to the Bush election campaign.

GE/Universal's United 93 was billed as the "true account" of how heroic passengers pn the plane "foiled the terrorist plot" by forcing it to crash prematurely in rural Pennsylvania. At the time, Bush's official 9/11 story was being seriously interrogated by America's independent news media; according to the results of a 2004 Zogby poll, half of New Yorkers believed "US leaders had foreknowledge of impending 9/11 attacks and 'consciously failed' to act"; and just one month prior to the release of United 93, 83 per cent of CNN viewers confirmed their belief "that the US government covered up the real events of the 9/11 attacks". With the official narrative under attack, the US government welcomed the release of United 93 with open arms: the film was a faithful audiovisual translation of the 9/11 Commission Report. Soon after its ­nationwide release date, President Bush invited representatives of Universal to the White House for congratulatory handshakes, followed by a private screening.

Munich, Steven Spielberg's exploration of Israeli vengeance following the Palestinian terrorist attack at the 1972 Olympics, could also be understood to reflect the interests of General Electric. Israel is one of GE's most loyal customers, buying Hellfire II laser missiles as well as propulsion systems for the F-16 Falcon fighter, the F-4 Phantom fighter, the AH-64 Apache attack helicopter, and the UH-60 Black Hawk helicopter. Spielberg ends his film with a lingering shot of the World Trade Center, its twin towers standing as monolithic reminders as to "why we fight", and casting a shadow over the 167 minutes of running time, the voice of the Palestinian cause is restricted to just two and a half minutes of dialogue. Far from being an "even-handed cry for peace", as one critic claimed, Munich is more easily interpreted as a corporate-backed endorsement of Israeli policy.

To understand what might happen if big business interests were less prevalent in the film ­industry, consider the independent distributor Lions Gate Films. Lions Gate was formed in Canada by an investment banker, but is not beholden to a multi-billion dollar parent corporation with multifarious interests. The result has been some of the most daring and original popular political cinema of the past ten years: American Psycho, which criticised corporate capitalism; Hotel Rwanda, which highlighted the fail­ings of US foreign policy, and Lord of War, which focused on the arms trade.

Jim Hightower, the radio commentator fired by Disney after criticising its policies on ­issues including tobacco advertising, once said that "the real political spectrum is not left to right, it's top to bottom, and the vast majority of people aren't even in shooting distance of the economic and political powers at the top".

As we peer up from our popcorn, it is worth remembering that behind the magic of the movies lurks the darker power of corporate ­public ­relations.

Matthew Alford is author of the forthcoming book "Projecting Power: American Foreign Policy and the Hollywood Propaganda System"

Robbie Graham is associate lecturer in film at Stafford College