The unions representing American and Southwest airlines pilots are asking lawmakers and the White House for an exemption or an alternative to the federal mandate requiring companies with more than 100 people to get vaccinated.

Roughly 30% of American Airlines pilots are not vaccinated, according to the Allied Pilots Association, the union representing American’s 14,000 pilots. Southwest's pilot union could not say how many of its members were unvaccinated.

"Some of APA’s members are unable to undergo vaccination for documented medical reasons, while others are reluctant to get vaccinated based upon concerns about the potential for career-ending side effects," union president, Captain Eric Ferguson wrote in a letter to more than 15 people at the DOT, White House, and Congress.

Commercial airline pilots adhere to strict medical requirements and some pilots fear vaccine side effects like blood clots or heart problems could prevent them from maintaining a medical clearance, thus ending their careers as pilots.

The CDC reports there have been more than 200 million doses of vaccine administered already in the U.S. and serious safety problems are very uncommon.

Most side effects from COVID vaccines are mild and temporary and include things like soreness at the injection site or fatigue, headaches, chills and nausea. These side effects usually go away within a day or two.

There have been rare adverse events of blood clots -- about 7 per million vaccinated women between 18 and 49 -- with the J&J vaccine. Women in that age range may want to select a different vaccine.

There have been a small number of temporary heart problems associated with Pfizer and Moderna vaccines for young men. These reports are rare and the known and potential benefits of COVID-19 vaccination outweigh the known and potential risks of getting COVID -- which include myocarditis or pericarditis.

The union representing Southwest’s pilot’s echoed American's request to the federal government, saying in a statement: "Our pilots have shouldered an elevated risk of illness from the start of the pandemic, including well before the vaccines became available. And we are hopeful that our contributions are recognized and accounted for as we seek approval of an alternate means of compliance and an operationally feasible implementation period."

Both unions say the 60-day-timeline for the requirement to get vaccinated could have a significant impact on holiday travel if pilots who choose not to get vaccinated are forced off the job.

"We are also concerned that the Executive Order’s anticipated 60-day implementation period for mandatory vaccinations could result in labor shortages and create serious operational problems for American Airlines and its peers. Airlines generate a substantial portion of their annual revenue during the holiday period, with a great many travelers depending on us to get them to their destinations. Our nation’s airlines, and the traveling public, cannot afford significant service disruptions due to labor shortages," Ferguson wrote in the letter.

Meanwhile, United Airlines says 98.5% of its employees are now vaccinated after the company mandated the shot. At least seven United employees are suing the company to avoid getting the vaccine.

Delta Air Lines will soon charge unvaccinated employees $200 more per month for health insurance. The company says at least 82% of its employees are vaccinated.