The Federal Aviation Administration is warning the US Congress not to raise the mandatory retirement age for airline pilots until the agency can study whether older pilots would raise safety risks. The House voted last year to raise the retirement age from 65 to 67 as part of a larger bill covering FAA operations.

FAA Administrator Michael Whitaker said in a letter to two key senators Monday that pilot fitness is critical to safety, and the agency should be able to create safeguards before raising the age limit.

Sen. Maria Cantwell, D-Wash., chair of the Senate committee that oversees aviation, endorsed the FAA’s position. Cantwell’s Senate committee is scheduled to take up its version of the bill this week.

“When it comes to raising the pilot retirement age, the FAA has made clear that a scientific and safety analysis must come first. That has not happened,” Cantwell said in a statement. “Aviation safety is paramount, and now is not the time to take a shortcut.”

The Biden administration has previously opposed raising the age limit. Raising the retirement age would put the United States out of step with other countries, and US pilots over 64 would not be allowed to work on international flights.

The Air Line Pilots Association has opposed raising the age limit, saying it would not increase the pool of pilots.

The Regional Airline Association supports the change. The association is a trade group for smaller airlines, which have faced shortages of crews and have been forced to raise pay to attract pilots.

The age limit is one of several contentious issues in a bill to reauthorize FAA programs for five years, including pilot training requirements and consumer-protection provisions.