U.S. officials are expressing concerns about Mexico’s handling of energy permits, raising allegations of preferential treatment for state-owned energy companies.

Secretary of State Mike Pompeo, Energy Secretary Dan Brouillette and Commerce Secretary Wilbur Ross wrote in a letter this week to Mexican officials that they were concerned by reports of “regulators who were allegedly instructed to block permits for private sector energy projects and to exercise their regulatory authority to favor state owned energy companies.”

“If true, this would be deeply troubling and raise concerns regarding Mexico's commitments under the [U.S.-Mexico-Canada Agreement],” the Trump administration officials added.

They also wrote that this could “adversely affect hundreds of millions of dollars of U.S. government public energy investments in Mexico.”

A spokesperson for the Mexican embassy declined to comment.

While U.S. officials are raising concerns over the energy dispute, Reuters reported this week that Mexican officials may also bring up their own concerns about agricultural trade with the U.S.

“It means we keep talking within the framework we signed, the free trade accord,” Economy Minister Tatiana Clouthier told the wire service. “And getting into a negotiation about what bothers one side, and what bothers the other.”

The dispute follows a report last month that separately warned about Mexico’s labor law implementation under the revised North American treaty.