Ofcom is to investigate whether the X Factor final earlier this month broke its broadcasting code following complaints that dance performances by Christina Aguilera and Rihanna were inappropriate for a pre-watershed show.
The singers gave a series of raunchy performances in the first part of the final of the Simon Cowell talent show, which was broadcast between 7pm and 9pm on Saturday 11 December.
Aguilera performed a raunchy routine with her dancers wearing only stockings, knickers and bras, while Rihanna stripped off her gown to parade around the stage in a bikini.
Ofcom and ITV received 2,750 and 1,500 complaints respectively about the show.
The media regulator will assess whether the show broke section 1.3 of the broadcasting code, according to which "children must be protected by appropriate scheduling from material that is unsuitable for them".
It will also investigate whether the show encouraged viewers to download songs by guest singers.
Ofcom's decision is expected in the New Year. If Ofcom finds that the show broke the broadcasting code, Simon Cowell may be forced to tone down next year's show.