Critics of T-Mobile’s newly approved merger with Sprint are particularly concerned about the impacts on rural Americans, who are often served by the two carriers. The fear is that merging the third and fourth-largest carriers into one will reduce competition and raise prices on rural consumers.

It’s a key concern in Oregon, home to vast swaths of sparsely populated regions. That’s why Oregon Attorney General Ellen Rosenblum is joining a multi-state lawsuit seeking to block the T-Mobile/Sprint merger.

“As a state with major metropolitan centers and rural areas, and a diverse economy, geography, and population, Oregon reflects the widespread nature of the harm that is likely to result from the anticompetitive merger of T-Mobile and Sprint,” the AG’s office said in a press release.

Ten states filed the original lawsuit in June claiming the merger would “eliminate the competition between Sprint and T-Mobile and will increase the ability of the three remaining [carriers] to coordinate on pricing.” The complaint also says the new company would “have reduced incentives to engage in innovative strategies to attract and retain customers compared to Sprint and T-Mobile today.”

As a state with major metropolitan centers and rural areas, and a diverse economy, geography, and population, Oregon reflects the widespread nature of the harm that is likely to result from the anticompetitive merger of T-Mobile and Sprint.

Last month, federal regulators approved the merger, paving the way for the two companies to combine under the T-Mobile brand. The approval came after months of touch-and-go discussions and some last-minute concessions. T-Mobile agreed to transfer assets to satellite TV provider Dish Network to create a new wireless carrier in an attempt to assuage concerns about competition.

But the states aren’t backing down. The original lawsuit claims the merger will cost residents in the plaintiff states more than $4.5 billion annually.

Earlier this month, a federal court in New York delayed the trial for the case to Dec. 9, Reuters reports. The states sought the delay so they could have more time to investigate the merger.

Notably, T-Mobile’s home state of Washington has stayed out of the fight. On other matters, Washington state has not been shy about suing the federal government. Washington Attorney General Bob Ferguson has filed 39 lawsuits against the Trump administration.

Update: Ferguson said he was still deciding whether or not to join the case in a statement to GeekWire.

“My office is still evaluating the information we have received from the parties,” he said. “I have not made a final decision as to whether to join a legal challenge to the merger.”