Oregon has agreed to join a multistate lawsuit aimed at blocking the merger of T-Mobile US Inc. and Sprint Corp.

It is the 15th state, in addition to the District of Columbia, to join the legal challenge.

"The current [merger] plan will result in reduced access to affordable wireless service in Oregon — and higher prices," said Oregon Attorney General Ellen Rosenblum.

Deutsche Telekom AG CEO Timotheus Höttges recently said the company is willing to engage with state attorneys general to work to resolve outstanding concerns about the merger of its U.S. unit and Sprint. The deal would bring together the No. 3 and No. 4 largest U.S. wireless network operators.

The U.S. Department of Justice conditionally approved the T-Mobile-Sprint deal in July after the parties agreed to divest some wireless assets to Dish Network Corp.