Published reports say a group of at least 10 state attorneys general are planning a lawsuit to block a $26.5 billion merger of wireless carriers T-Mobile and Sprint.
It's an unusual step ahead of a decision by federal antitrust authorities.
The reports from Reuters and The Wall Street Journal cite unidentified people familiar with the matter.
The Justice Department has not yet issued a decision. The Republican chairman of the Federal Communications Commission, the nation's telecom regulator, supports the deal.
The companies say they need to bulk up to upgrade to a fast, powerful "5G" mobile network that competes with Verizon and AT&T. The companies are appealing to President Donald Trump's desire for the U.S. to "win" a global 5G race. Consumer advocates and Democratic lawmakers worry about price increases and job cuts.