Several hundred thousand public sector workers are to take to the streets on Thursday as they challenge the government over proposed pension changes.
Up to 400,000 people will protest over the new scheme, which they say will cost them more and leave them working longer for smaller pensions.
Among them will be about 20,000 off-duty police officers, immigration staff, lecturers, civil servants, health workers, and members of the Royal Fleet Auxiliary. Picket lines will be put up outside jobcentres, airports, and government buildings.
The Unions taking part have said that the protests were part motivated by Wednesday's Queen's Speech, which made clear the goverment was going ahead with their plans for pension changes.
The government has said that existing pension schemes are unfair and no longer affordable.
The industrial action is expected to be much smaller than similar protests back in November, but will be the largest police rally since 2008.