The X Factor is to be investigated by TV watchdog Ofcom over concerns that it encouraged viewers to download songs by guest stars Diana Vickers and Michael Bublé.
The regulator is to examine whether the show broke rules in the broadcasting code on references made to commercial products.
An Ofcom spokesman said: "We are investigating the X Factor for potential breaches of our rules prohibiting the promotion of products in programmes."
The media regulator is to examine two episodes of the show.
On October 17, when Vickers – a former X Factor contestant – performed, host Dermot O'Leary told viewers: "If you want to download Diana's single, the details are at ITV.com/XFactor."
He made the same remark on the night of Canadian star Bubl's performance on October 24.
Under broadcasting rules, products and services must not be promoted in TV programmes.
The rule does not apply to programme-related material, which means that the practice is legitimate when it concerns X Factor contestants but not when it relates to the promotion of guest acts.
The investigation, launched after Ofcom officials noted the references, is the latest controversy to hit the show.