NATIONWIDE -- At least 100 flight attendants of just one of the world's largest airlines have tested positive for the coronavirus, a major flight attendants union says.

• Union says 100 American Airlines flight attendants have had COVID-19
• Association of Professional Flight Attendants represents 27,000 members
• Major airlines have declined to release specific numbers among crews

The Association of Professional Flight Attendants, which represents more than 27,000 flight attendants, said in a message to its members that American Airlines has "agreed to start providing face masks for frontline team members while at work should you choose to wear one," CNN reports. The union's message said masks were being distributed this week.

Fort Worth-based American was the world's largest carrier last year in terms of number of employees, planes in its fleet (around 950), daily flights, and destinations, according to The Dallas Morning News. But Delta Air Lines and United Airlines aren't that far behind.

None of the major carriers have released specific numbers of COVID-19 cases among employees, though United and Delta confirmed that staffers had tested positive.

"We continue taking aggressive and proactive steps to ensure all of our employees are safe, following CDC guidelines," said a statement from United, which acknowledged that some of those staffers are crew members.

Delta stressed that if a crew member tests positive, it works with the Centers for Disease Control and Prevention to determine next steps, including contact-tracing and notifying anyone who might have been close contact with that crew member.

"Nothing is more important than the safety and health of our people," a Delta spokesperson tells Spectrum News. "Our comprehensive notification process follows -- and in some cases exceeds -- CDC guidance."

American, for its part, doesn't dispute the flight attendants union's figure of 100 and said it has been working closely with the CDC and health officials on safety measures.

"We continue to look at all ways we can care for -- and protect -- our team during this stressful time," a statement from American said.

As for specifically pilots, the Air Line Pilots Association, International confirmed it's tracking cases among its pilots but isn't releasing those numbers.

Dallas-based Southwest Airlines and South Florida-based Spirit Airlines both declined to confirm COVID-19 cases among its crew members or employees, citing medical privacy.

Spirit said anyone who contracts COVID-19 will be supported and released from work duties to seek care and quarantine. Southwest said it "follows all CDC notification guidelines for any confirmed case."