Skittish about buying a nonrefundable plane ticket given the growing travel fallout from the coronavirus epidemic? 

American Airlines, Delta Air Lines, United Airlines and other carriers, worried about soft ticket sales, are taking the unprecedented step of broadly waiving those hefty ticket change and cancellation fees for new ticket purchases.

JetBlue started the trend last week because of "evolving coronavirus concerns'' and was quickly joined by Alaska Airlines, which calls it a "peace of mind'' waiver.

American was the first of the big three U.S. airlines to announce a fee waiver, on Sunday.

On Monday, Delta joined the club, but with a twist: its fee-free waiver only applies to international flights while the other carriers' policies include those flights and flights within the United States.

"We realize customers have questions about the ongoing COVID-19 or coronavirus outbreak and the possibility of further government travel restrictions,'' the airline said in announcing the policy.

On Tuesday, United added its own waiver for new tickets. 

"We know people are taking a second look at their travel plans right now, and we want you to have flexibility when planning your next trip,'' the airline said in announcing the new policy.

At least one lawmaker thinks the airline's waivers don't go far enough. Sen. Richard Blumenthal (D-Conn.) on Tuesday urged airlines to allow travelers holding any tickets, regardless of when they were purchased, to change or cancel their tickets without paying a change fee.

Southwest Airlines, the country's largest domestic carrier, is the only major U.S. airlines that doesn't charge change fees. Travelers can cancel or change any Southwest ticket, even those that are nonrefundable, and receive the value of the ticket for future travel.

Anxiety abounds: Coronavirus fears putting vacations in limbo 

How do these free changes work? And are they really free?

There is fine print, of course. The biggest, in all the change-fee waivers to date: you can't buy a nonrefundable ticket under this policy and request a refund if your plans change or you don't want to travel. You can change or cancel the ticket for free. If you cancel, you'll receive credit for a future flight.

An airline-by-airline look:

American Airlines: American's waiver allows travelers who purchase tickets between March 1 and March 16 to change or cancel them without paying fees that start at $200 per person. The new policy covers tickets purchased for travel through late January 2021. 

On American, the fee will be waived for changes made up to 14 days prior to travel. So if you buy a ticket for a summer trip and need to change it for lingering coronavirus concerns or any reason, you just have to change it at least two weeks before departure to avoid the fee. 

Fare differences will apply: If you nab a $250round-trip ticket from Chicago to Orlando and the going rate is $400 when you change the ticket to another date, you'll pay an extra $150.

Delta Air Lines: Delta's waiver covers travelers who buy tickets between March 1 and  March 31 for international travel, including Puerto Rico and the U.S. Virgin Islands. Flights within the U.S are not covered. Tickets can be purchased for travel as far out as February 2021. Fare differences apply to changed tickets. 

United Airlines: United's waiver covers travelers who buy tickets between March 3 and March 31 for travel to any destination. Travelers can change their ticket to another flight (fare differences apply) or cancel the trip and receive a credit that is good for a year from the date the ticket was purchased.

JetBlue Airways: JetBlue's temporary change fee waiver, which applies to tickets purchased between Feb. 27 and March 11, covers travel through June 1. Travelers will receive credit for a future flight. Fare differences will apply on the new tickets.

Alaska Airlines: Alaska's waiver covers tickets purchased Feb. 27 through March 12 for travel through June 1.  Fare differences will be apply on any changes. 

British Airways: British Airways' "Book with Confidence'' policy covers tickets purchased between March 3 and March 16. Changes can be made any time before departure, but any fare difference will apply.