SAN JOSE (KPIX) — Air traffic controllers warned travelers Thursday that there will be flight delays that could worsen if the government shutdown continues.

“You’ve (already) heard delays that weren’t associated with weather,” said National Air Traffic Controller Association president Scott Conde. “If you don’t have enough people you can’t work the same number of airplanes.”

Conde said the delays could result in a similar number of planes which sat on the tarmac during the 2013 government shutdown when as many as 6,500 planes per day didn’t take off on-time.

The warning isn’t as dire as the one made by the Association of Flight Attendants and the Association of Professional Flight Attendants. Those unions, which represent thousands of flight attendants, sent a letter to President Donald Trump, House Speaker Nancy Pelosi and Sen. Majority Leader Mitch McConnell that read in part: “Our members and the traveling public are flying within a system that is less safe and secure as long as the shutdown continues.”

A Bay Area air traffic controller, who did not want to be identified, told KPIX they are being forced to work during the shutdown and many are working overtime because they are short-staffed.

Training of new air traffic controllers has also come to a halt and engineers who fix their equipment are being told to stay home. Thursday was the first day they did not get a paycheck.

“We are highly paid professionals who will ensure that the people who get on those planes are safe but that margin of safety degrades if we’re distracted,” Conde said.

He said many will resign if the shutdown continues because they simply can’t afford to survive in the Bay Area without a paycheck.

An FAA spokesperson released a statement that said in part: “We are allocating FAA resources based on risk assessment to meet all safety critical functions.”

But the strain is expected to create a backlog of work and put more pressure on air traffic controllers who are left, causing a ripple effect throughout the country.

“We operate the safest, most efficient, most complex airspace in the world and to use those people as political pawns over government funding is wrong,” Conde said.