The fumes were reported about 10 a.m., and firefighters ordered the tower cleared, airport spokesman Robert Yingling said. He said the fumes were coming from a work site at the airport's main terminal.
"People in the tower started to feel ill because of a strong smell of fumes," Kieron Heflin, president of the Dulles Tower National Air Traffic Controllers Association, told CBS Radio affiliate WTOP.
No flights were affected, he said. The tower was being ventilated, and workers exposed to the fumes were being evaluated.
Laura Brown, a spokeswoman for the Federal Aviation Administration, said the air traffic controllers were moved to another tower that is normally used to coordinate planes at airport gates.
Both towers have the same capabilities, though the backup tower has fewer work positions, Brown said.
The union chief disagreed.
The ramp tower that doesn't contain all the equipment they typically use, Heflin said. That equipment includes wind indicators and ground radar displays.
"We really have no procedures for working out of the ramp tower," he said.