Culture Secretary Lisa Nandy has said she is "minded to intervene" in the proposed £1.6bn deal for Sky to buy ITV's media and entertainment division.
Nandy said there were reasonable grounds to believe the deal could affect free expression in the media and the variety of Britain's news landscape.
Sky said it would "carefully consider" a letter from the culture secretary and "engage constructively" with the review into the deal.
"We remain confident that bringing Sky and ITV's media and entertainment business together will create a stronger British media," it said.
ITV welcomed the letter and said the deal would help it "compete with global streaming platforms, benefiting viewers, advertisers and the UK creative industries".