Michigan Attorney General Dana Nessel has joined a group of state attorneys general filing a lawsuit to block T-Mobile's $26.5 billion bid for Sprint, citing consumer harm.
The suit filed in New York Federal Court alleges the merger will drive prices for cell service up and eliminate competition for customers.
"We cannot sit idly by while two of the biggest companies in the country attempt to join forces," said Nessel, adding the merger would drive prices higher by nearly 10 percent.
Nessel says she intends to protect Michigan residents, "from a move by corporate players that will enrich their shareholders on the backs of their customers."
Michigan joins nine other attorneys general in trying to stop the merger.
It's an unusual step ahead of a decision by federal antitrust authorities. The Justice Department's decision is pending. The Republican chairman of the Federal Communications Commission 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.
Nessel said she's also concerned about the impact on low-income customers who rely on prepaid cell service.
She's concerned that many families will see their cellphone service suspended or even cancelled because of price increases, leaving them without options.
New York and California filed the lawsuit and were joined Tuesday by attorneys general from Connecticut, Colorado, the District of Columbia, Maryland, Mississippi, Virginia and Wisconsin, along with Michigan.