Delta Air Lines, facing mounting pressure from employees who said their uniforms are making them sick, will issue an entirely new garment line for its flight attendants and airport customer service agents by late next year.

The Atlanta-based airline promises the new line will be better than the current uniforms, which have been in use for less than two years. The Zac Posen-designed garments were celebrated upon launch in May 2018, but many flight attendants, gate and ticket agents said they quickly began experiencing adverse health effects from the apparel.

Delta, the dominant carrier at Minneapolis-St. Paul International Airport, has faced withering public criticism, lawsuits and workers’ compensation cases in recent months. Employees, who reported health issues ranging from hives to headaches to severe breathing problems, allege the company was not doing enough to help them find alternative uniforms that didn’t make them sick.

As of November, about 3,000 flight attendants had formally reported adverse health effects attributed to the uniforms. That same month, the airline streamlined its uniform-complaint process, but it was too little too late for many flight attendants. A group of 536 workers, including dozens in Minnesota, filed a class-action lawsuit against Delta’s uniform manufacturer, Lands’ End of Dodgeville, Wis.

“In response to our employees, we’ve taken steps over the past few months to address feedback received about the uniform, including offering alternative garments, hiring fabric experts, and conducting comprehensive chemical testing,” Ekrem Dimbiloglu, director of Delta’s new uniform program, said in a statement. “This is a big decision, but we side with our people, and we are making a change.”

Delta said it will enlist the help of its employees through the design and testing phase for the new uniforms, and will look for more sustainable textile practices as well as “taking greater control of the production process,” the company announced Wednesday evening.

A single chemical has not been identified as the definitive culprit making the workers sick. Medical doctors and environmental toxicologists said the cause can be difficult to pinpoint given the wide variety of compounds, allergens and heavy metals found in modern textiles that often are added to elicit a desired attribute, such as antimicrobial, stain repellent or anti-wrinkle.

Once flight attendants started reporting health problems, Delta hired a third-party toxicology firm, Intertox, to test the uniforms. The airline published the findings, concluding that the garments were below the OEKO-TEX Standard 100, a key chemical standard, except for the in-flight apron, which tested high in a compound called PFOA. U.S. manufacturers like 3M and DuPont claim to have stopped making PFOA and PFAS, yet research shows their persistence in the environment. The union also points to the complexities of a global supply chain and the challenges of tracking every treatment applied to a garment.

Delta’s new uniforms will be certified and labeled with the OEKO-TEX Standard 100 seal, the textile industry’s highest standard for chemical testing.

Ben Mead, managing director of Hohenstein Institute America Inc., a founding member of the OEKO-TEX Association, said the Standard 100 is something that should be considered beforehand, not after the clothing is made.

“We would see Standard 100 as a proactive solution, not something done after the fact,” he said. “The difference being that if something is certified, it is not only tested, but throughout the design process, we are actually gathering information on all of the inputs that have gone into the fabrics, and ensuring that not only are they meeting the requirements, but there is a system in place for those producers to meet those standards day in and day out.”

Additionally, a uniform manufacturing contract typically runs five to seven years, so ongoing oversight is important, he said. The OEKO-TEX certification requires that those garments be resubmitted every year to maintain their certification, Mead said. OEKO-TEX is constantly surveying global legislation, new testing methods in the industry and new research on hazards, as well as overall textile sustainability.

“All that to say,” Mead said, “the standard that’s in place in 2015 is very different from what it is today because new limits are constantly being set and new methods employed.”

That proactive approach is something Delta said it will do this time around.

The current uniform line is worn by about 65,000 Delta workers — 35,000 of whom are what’s called “above wing,” or those who interact directly with customers, like flight attendants and airport customer service agents.

Delta’s “below wing” workers, or those who work jobs primarily on the tarmac or behind the scenes at the airport, compose the remaining 30,000. Their garments were made of different materials and few complained of adverse health effects. The airline will introduce some new options for its below-wing workers but it won’t swap out an entirely new line.

Until the new uniforms are ready, Delta is making a couple of basic OEKO-TEX Standard 100 Certified items available for all flight attendants who wish to get out of the current uniforms sooner.

The issue has driven a wedge between the company and some of its longtime crew members at a time when the Association of Flight Attendants-CWA is trying to unionize Delta’s flight attendants. The health effects mimic similar problems experienced by American and Alaska airlines’ flight attendants.

Both of those groups are unionized.

“We applaud this step in the right direction, but encourage Delta management to take additional actions as soon as possible for the health of all flight attendants and to repair the damage caused for individuals,” Sara Nelson, president of AFA-CWA international, said in a statement.

AFA is urging Delta to stop using the existing uniforms and provide the basic black-and-white alternatives to everyone, aiming to avoid exposure for those who are sensitive and prone to reactions. The union also is asking Delta to provide pay and benefits for employees with physician-diagnosed health problems until they are able to return to work.