FILE PHOTO: A smartphones with Sprint logo are seen in front of a screen projection of T-mobile logo, in this picture illustration taken April 30, 2018. REUTERS/Dado Ruvic/Illustration

WASHINGTON (Reuters) - T-Mobile US Inc's TMUS.O proposed $26.5 billion tie-up with Sprint Corp S.N won formal approval from the Federal Communications Commission on Wednesday in a vote split along party lines, two sources told Reuters.

Chairman Ajit Pai and two Republican commissioners voted to approve the deal while two Democratic commissioners voted against it, the sources said.

The text of the approval order is not expected to be released until later in the month.

The deal to combine the third and fourth largest U.S. wireless carriers, which has been fighting for government approval since April 2018, still faces a lawsuit brought by a group of state attorneys general, headed by New York.

The lawsuit against Sprint and its parent company Softbank Group Corp 9984.T and T-Mobile and its parent Deutsche Telekom AG DTEGn.DE argues the deal will lead to higher prices for consumers. A trial date has been set for Dec. 9.

The U.S. Justice Department approved the deal in July.

Under the Justice Department deal, the companies would divest Sprint's prepaid businesses, including Boost Mobile, to satellite television company Dish Network Corp DISH.O, and provide it with access to 20,000 cell sites and hundreds of retail locations. That deal is worth about $5 billion.