When American Airlines flight attendants began to complain about the company’s new uniforms, the airline shrugged off the problem, saying it was limited to about a dozen people with allergies to wool.

But a union for flight attendants with the world’s largest carrier says the number of employees complaining about hives and headaches after wearing the uniforms has grown to more than 1,300.

In addition, the Association of Professional Flight Attendants had the uniforms tested and found they contained detectable levels of chemicals normally found in pesticides, fungicides and fertilizers.

The uniforms, produced by the corporate clothes maker Twin Hill, rolled out in September, representing the first new uniforms for American’s employees in about 30 years.

“We will continue to invest the resources necessary to get to the bottom of this and we fully expect the company and Twin Hill to do the same,” the union told its members in an online notice last month.

American Airlines officials say the number of complaints represent only about 1 percent of the 70,000 employees who are wearing the new uniforms. Still, the airline has tested the uniforms twice and is waiting for the results from a third test.

“We want our employees to be happy with their new uniforms,” said American spokeswoman LaKesha Brown, adding that employees have the option of wearing their old uniforms if they have a problem with the new version.