Clothing manufacturer Twin Hill has come to the defense of its ill-received American Airlines uniforms, penning a letter to the Association of Professional Flight Attendants (APFA) in wake of numerous complaints from flight attendants that the uniforms are making them sick.

American began rolling out the new uniforms to frontline workers, including flight attendants, back in September. Within a month, hundreds of flight attendants had complained to their union and management about adverse effects, including rashes and headaches.

Monday's letter from Twin Hill senior vice president and managing director Daryl Stilley calls into question the legitimacy of the APFA's claims, encourages the group to take part in the testing process and reveals it's developing a third alternative for those employees still experiencing sensitivity.

"Many of your public statements, in particular, have been both inaccurate and damaging to Twin Hill 's reputation," wrote Stilley. "We were deeply concerned when claims made by the APFA started to surface about your members having reactions to the American Airlines uniforms provided by Twin Hill, and we immediately leveraged every resource at our disposal to investigate those claims."

READ MORE: Problematic New American Airline Uniforms Lead To Union Grievance

The letter confirms that Twin Hill had the uniforms tested for restricted chemicals at an independent lab and that American has already made a non-wool alternative uniform available to its workers.

"We are now working on designing entirely new 100 percent cotton garments as a third alternative," added Stilley. "We are committed to ensuring that every single AA employee has a uniform that is both safe and comfortable."

"Given the health reactions you assert your members are facing, we anticipate that you will not delay scheduling your visit to our distribution center any longer."

Twin Hill's letter comes less than one month after the union representing American Airlines employees filed an official grievance with the airline calling on the airline to ditch the new look and pitch in for workers' medical expenses for health problems stemming from the uniforms.

Follow @_Pat_Clarke