From oozing blisters and wheezing to rashes, itchy eyes, and sore throats, numerous American Airlines Group flight attendants say their new work uniforms are making them sick.

But after a battery of tests and a tense back-and-forth among their union, the airline, and the uniform supplier, it’s still not clear what exactly is behind the rise in health complaints.

The Association of Professional Flight Attendants, which represents flight attendants for American, has asked the carrier to recall the new garments, which went to 70,000 employees starting in September.

The airline says it has spent more than $1 million for three rounds of toxicological tests that, so far, haven’t turned up any obvious causes for the maladies.

American and the union are now conferring on protocols for further examinations – but the issue grew more contentious last week amid a flurry of communications among the airline, the flight attendants’ union, and the uniform supplier.

The union says about 10 percent, or 2,300, of the flight attendants it represents have reported adverse reactions-among them skin rashes, sore throats, wheezing, fatigue and vertigo-since they started wearing the new uniform. “This continues to be a serious and growing problem, and is not going to go away without some further remedial action by the company,” the union said on Thursday in a message to members.

American says an employee call center it opened in October has gotten 450 formal complaints of health problems, 350 of them from flight attendants.

The uniform controversy has become such a topic of concern at the airline that several executives have begun wearing the outfit, or parts of it, in an effort to allay fears.

Still, the flight attendants believe that chemicals in the uniform – say, a dye or an adhesive – are probably causing the severe reactions the union says are affecting roughly one in 10 flight attendants.

“I’m very confident that there’s something in that fabric that’s causing this,” said Bob Ross, the union’s national president. “Some (people) react right away. Lots of other people are feeling the effects just by being around the uniforms.”

Ross, a 33-year American veteran, said he himself wore the new uniform’s cotton shirt, “and by the end of the day my entire chest, neck, and arms were red.” It took two showers and disposal of the shirt and its packaging to resolve, he said.

A New York-based flight attendant, speaking via online chat on condition of anonymity, said her throat had begun burning on one flight and that she had grown hoarse and broken out in hives. She said she had been to 12 doctor appointments in 40 subsequent days for tests and consultations.

The uniforms have undergone a battery of tests, and the union, airline, and supplier Twin Hill have all hired experts to determine the chemical composition of the uniforms.

So far, testing by American and Twin Hill have not turned up substances that aren’t supposed to be in the clothes or any chemical levels exceeding safety limits, the airline has said.

The union has hired its own toxicologist to examine the results. It has spent more than $20,000 so far and wants American to reimburse it for its expenses, Ross said.

Last week, the airline denied a grievance Ross had filed on behalf of sick attendants. “The safety and comfort of our team members is more important than anything we do, and we know it is at the forefront of the APFA’s mission too,” wrote Cindi Simone, American’s managing director of labor relations.

American has also reimbursed flight attendants who have bought new work clothes similar to the uniform.

It says employees may wear their old uniforms, though many no longer have one.

The public contretemps has prompted supplier Twin Hill to complain that it is being maligned unfairly.

In a Jan. 9 letter to Ross, an executive at the Houston-based supplier, a unit of Tailored Brands Inc., denied any problems with the 1.4 million garments it had provided, citing tests by an independent laboratory it hired.