The State of Oregon joined a lawsuit pushing for T-Mobile US’ proposed merger with Sprint to be blocked, as opposition against the deal from US states continued to ramp.

In a statement, the New York Attorney General’s office, which is leading the lawsuit along with California, said Oregon became the 15th state to join the action to block the “anticompetitive” merger.

New York attorney general Letitia James said Oregon’s inclusion added to the states’ momentum and was particularly significant because it means “there isn’t a single region of this country” which doesn’t oppose the merger.

With Oregon, the lawsuit is backed by 15 states and the District of Colombia, representing almost half of the US population. Texas joined the action at the start of the month.

“We remain committed to blocking the merger of T-Mobile and Sprint because it would be bad for consumers, bad for workers and bad for innovation,” added James.

Oregon’s attorney general Ellen Rosenblum said it was important for the state to oppose the merger.

“If left unchallenged, the current plan will result in reduced access to affordable wireless service in Oregon, and higher prices. Neither is acceptable,” she said.

T-Mobile’s proposed merger with Sprint won approval from the US Department of Justice (DoJ) in July, after the companies agreed to sell-off Sprint’s prepaid business to TV provider Dish Network to ease competition concerns.

While DoJ approval was crucial, moving the deal a step closer to completion, state opposition remains a major stumbling block.

A court case to hear objections from the states is due to be held in December.