FILE PHOTO: People walk past the AT&T store in New York's Times Square, New York, U.S., June 17, 2015. REUTERS/Brendan McDermid/File Photo

WASHINGTON (Reuters) - Seven groups ranging from the Tea Party Patriots to liberal consumer groups warned against AT&T's T.N plan to buy Time Warner TWX.N in a letter to Attorney General Jeff Sessions, saying the deal could give one company too much power over what Americans see on television.

The letter is signed by officials from the more liberal Public Knowledge and Consumer Federation of America as well as Tea Party Patriots and American Family Association, which opposes homosexuality.

“While the undersigned groups’ opinions diverge significantly on many policy issues, we are united in our desire to ensure that free expression is not threatened by an increasingly limited number of companies that dominate U.S. media,” the groups said in the letter.

AT&T, the No. 2 wireless carrier which already owns satellite television service DirecTV, is in the process of buying Time Warner Inc for $85.4 billion in an effort to turn itself into a media powerhouse that can bundle mobile service with video. It has said it expects the deal to close by the end of the year.

Owning DirecTV makes AT&T the top pay-TV firm. Combining that clout with Time Warner, which owns HBO, CNN and the movie studio Warner Brothers, would make AT&T even more powerful, the seven groups warned.

The groups expressed concern in particular that AT&T could create incentives for its customers to only watch its shows by not counting AT&T content against data caps. Or, the groups said, AT&T could relegate channels it does not own to undesirable channel locations.

Signatories also include officials from Americans for Limited Government, Frontiers of Freedom and Writers Guild of America West.