California’s Public Utility Commission in San Francisco announced Thursday it would open an investigation into AT&T’s merger with T-Mobile USA, the first state to begin a formal probe into the deal.

Sprint, which wants regulators to block AT&T from acquiring T-Mobile, asked California’s utilities commission last week to launch an inquiry into the deal.

“We believe a thorough investigation will reveal the negative implications for pricing, choice and innovation, critical to California’s economy,” Sprint spokesman John Taylor said in a statement.

AT&T says its merger with T-Mobile would allow it to expand LTE access in California, and that the deal will ultimately benefit the state’s residents.

“As the federal review process continues, we’re confident in the merits of this deal and that regulatory approvals will be obtained after a thorough review of the facts and law because of the significant consumer, public, and economic benefits it brings,” AT&T spokesman Lane Kasselman said in a statement.

Sprint has also filed paperwork in West Virginia and Louisiana requesting investigations into the merger’s effect on the states’ residents.

West Virginia has not yet taken any action on Sprint’s request. The Louisiana Public Service Commission said last week it would allow the public to file comments on the merger, but did not open an investigation into the deal.

It is not clear whether states have any jurisdiction over the merger, which is being reviewed by the FCC and the Justice Department.