These are the airlines dropping mask mandates after a Trump-appointed judge struck down the requirement

• On Monday, a federal judge struck down the CDC's mask mandate for planes and transit agencies.
• Following the ruling, the US' four largest airlines dropped the mask mandate, making them optional.

Several US airlines and train systems have dropped their mask mandates after a federal judge on Monday struck down the Centers for Disease Control and Prevention's face-mask mandate for airplanes and public transit.

The requirement was put implemented by the Biden administration in February 2021 and had been extended multiple times and challenged in court.

Here are the airlines that dropped their mask mandate:

Alaska Airlines

"It has been a long 24 months with nearly constant change. I could not be prouder of our frontline employees who have handled every pivot focusing on safety and the care we're known for,"Alaska Airlines vice president of safety and security Max Tidwell said in a statement on Monday. "We're also thankful for our guests who remained considerate, patient, and stood by us throughout every twist and turn."

United Airlines

In a statement, United Airlines announced the same and added that masks were now optional.

"Effective immediately, masks are no longer required at United on domestic flights, select international flights (dependent upon the arrival country's mask requirements), or at US airports," the company said in a statement.

Southwest Airlines

Southwest Airlines also announced in a statement that "Southwest Employees and Customers will be able to choose whether they would like to wear a mask, and we encourage individuals to make the best decision to support their personal wellbeing."

American Airlines

American Airlines also followed suit, adding that "face masks may still be required based on local ordinances," meaning that the US' four largest airlines have all dropped the mandate.

JetBlue Airlines

JetBlue also announced it was moving away from the requirement, joining the big four airline companies.

"In line with Monday's federal court ruling and the Transportation Security Administration's guidance, mask-wearing will now be optional on JetBlue," per the company. "While no longer required, customers and crew members are welcome to continue wearing masks in our terminals and on board our aircraft."

Amtrak

According to CNBC, transit agencies are figuring out whether or not they will enforce CDC guidelines. Amtrak told Insider in a statement that the agency will no longer require masks for passengers and employees boarding and riding on their trains, adding that "Anyone needing or choosing to wear one is encouraged to do so."

The mandate overturned

On Monday, Judge Kathryn Kimball Mizelle, a Trump-appointed judge, wrote in her ruling that the CDC overstepped its powers with the initial guidance.

"Our system does not permit agencies to act unlawfully even in pursuit of desirable ends," she said in the ruling. The Biden Administration later announced that the Transportation Security Administration would stop enforcing the mandate, while it is still unclear if the Justice Department will appeal the decision.

"We're reviewing the decision and going to decline to comment any further," Danielle Blevins, spokeswoman for the agency, told Insider.

The ruling has largely put the onus on individual airlines, customers, and transit agencies to decide on how to enforce guidelines as companies and agencies brace to see whether the government will appeal.