FILE PHOTO: U.S. Transportation Secretary Sean Duffy announces actions against states for failing to enforce English language requirements for commercial drivers, during a press conference at the U.S. Department of Transportation in Washington, D.C., U.S., August 26, 2025. REUTERS/Brian Snyder/File Photo

By David Shepardson

(Reuters) -U.S. Transportation Secretary Sean Duffy on Wednesday warned European governments against imposing unilateral restrictions on transatlantic travel, saying Washington is prepared to enforce international agreements - a stance underscored by recent action taken against Mexico over similar concerns.

"We're seeing more airports get in the game of trying to restrict air traffic, which is contrary to the agreements that we have with them," Duffy told Reuters from Montreal where he is attending an international aviation meeting, citing concerns about Amsterdam, Lisbon and Dublin.

"It's important for commerce, for trade, for the movement of people in business, that we keep these flights open," Duffy said, questioning the validity of noise data to justify flight cuts.

Duffy in July ordered Mexican carriers to file U.S. flight schedules and could disapprove flight requests from Mexico if the government failed to address U.S. concerns. Earlier this month, he ordered Delta Air Lines and Aeromexico to unwind a joint venture by January 1.

U.S. airlines have raised concerns about noise reduction flight caps at Amsterdam Schiphol airport as well as a passenger cap at Dublin airport that is on hold pending a legal challenge. A Dutch court last year ordered the government to do more to cut noise pollution. JetBlue Airways last month told USDOT that "it is clear that an access problem exists for U.S. carriers in Lisbon" and warned it could pursue legal action for access.

Duffy said the administration's actions on Mexico were also aimed at Europe. "I think Mexico is a sign that we're not going to take that," Duffy said. "We're not at a place where we need to apply pressure."

Duffy said the requirement that Mexico file flight schedules "is a sign that we are willing to take additional action if they don't come into compliance with our open skies agreement." Asked about Delta's criticism of the decision, he said he understood the carrier's position on the Mexico JV but said it will probably be happy that "we are standing up for the agreements that we have globally."

(Reporting by David Shepardson in WashingtonEditing by Matthew Lewis)