“This merger would significantly decrease competition for mobile wireless telecommunications services in Illinois and across the country,” Illinois Attorney General Kwame Raoul said in a statement. “With fewer companies competing, customers would face fewer choices, higher prices, less innovation and lower quality service. I am proud to stand with my counterparts in taking action to protect consumers.”

T-Mobile last week responded to the lawsuit by saying that Sprint is unlikely to be a meaningful competitor as a standalone wireless company in the coming years because it’s struggling financially on multiple fronts with no end in sight.

Sprint has been steadily losing subscribers and market share, while struggling with a “huge debt load” and cash flow that’s been overwhelmingly negative, T-Mobile said in a court filing on Aug. 28 in Manhattan.

“Plaintiffs’ prediction that Sprint would abruptly reverse this long trend and emerge as a vigorous standalone competitor is nothing more than wishful thinking,” T-Mobile said. “Plaintiffs are dwelling in the past while the rest of the world is building super highways.”

T-Mobile and Sprint won approval from the U.S. Justice Department’s antitrust division after agreeing to sell assets to Dish Network. Even after the deal was approved, more states joined the lawsuit.

The states said in court filings that the Dish deal, intended to create a new rival in the market and preserve competition, was a “fig leaf” that wouldn’t really help consumers.

A trial is scheduled for December.

With Bloomberg