The United States has downgraded Mexico’s aviation rating from Category 1 to Category 2. That will prevent Mexican airlines from adding new U.S. flights.

The Federal Aviation Administration (FAA) announced the downgrade Tuesday, saying that Mexico failed to meet minimum international air-safety oversight standards. But promised to help the country’s aviation agency resolve areas of non-compliance.

Mexican airlines can continue existing services to the United States, though they will face increased scrutiny, but the downgrade bars them from adding new flights and prevents U.S. airlines from code sharing with flights operated by Mexican carriers.

Mexico’s transportation agency said it’s committed to working with the FAA to bump its rating back up to Category 1. But added in a public statement that the audit was carried out during a coronavirus outbreak last October when staffing was significantly reduced.