Both sang while scantily clad before 9 p.m., when kids were still tuned in.

X-Factor is under investigation by UK regulatory arm Ofcom after airing racy Rihanna and Christina Aguilera performances during what is supposed to be a family-friendly hour.

The U.K. Telegraph reports that Ofcam, which serves as a British FCC, received 2,750 complaints, and the network, ITV, received 1,500.

On the Dec. 11 finale, which was watched by 14 million viewers, a scantily-clad Aguilera sang two songs from Burlesque while grinding with female dancers and chair dancing. Rihanna then sang "What's My Name," stripping down from a gown to a bustier. Both performances aired between 7 and 9 p.m., before the so-called "watershed" hour, when children stop watching.

The number of complaints doubled after the U.K. Daily Mail wrote a column last Tuesday, with a columnist calling out the network for airing "sex-crazed nymphs before the watershed."