WASHINGTON — Top Democratic lawmakers have urged Treasury Secretary Steven Mnuchin to quickly provide American airlines with direct payroll assistance and to avoid insisting on overly restrictive terms that could deter companies from taking the money.

Major airlines began submitting their applications for government support to the Treasury Department on Friday but there is growing concern within the industry that Mr. Mnuchin will demand strict terms to ensure that taxpayers are compensated, such as large equity stakes in the companies. Some of the airlines, which have seen demand plummet as the coronavirus pandemic has stalled global travel, are wary of giving the government too much control over their businesses and accepting strict conditions tied to the aid.

Democrats fear that if Mr. Mnuchin drives too hard of a bargain, airlines will balk and lay off more workers. In a letter that was sent to Mr. Mnuchin on Sunday, Senator Chuck Schumer of New York, the Democratic leader, and Speaker Nancy Pelosi warned that it would not be in the public interest if the airlines were to choose to declare bankruptcy.

“Assistance must not come with unreasonable conditions that would force an employer to choose bankruptcy instead of providing payroll grants to its workers,” they wrote in the letter, which was reviewed by The New York Times on Sunday.