A source with knowledge of negotiations said airports, themselves facing billions of dollars in losses, are expected to request $10 billion in federal assistance.

Also Monday, some 60 of the world's air carriers, representing more than half of airline capacity globally, made an unprecedented and urgent plea for government assistance.

Their plea, made through the three biggest international airline alliances, which allow partners to share booking arrangements, urged "governments worldwide to prepare for the broad economic effects from actions taken by states to contain the spread of COVID-19, and to evaluate all possible means to assist the airline industry during this unprecedented period.”

They echoed previous calls to suspend "use-it-or-lose-it" rules that set a minimum level of service at capacity-constrained airports, or else airlines lose those "slots." The FAA has already done so at several U.S. airports through May, but the alliances hope regulators will consider extending suspensions through the summer.

They also asked other parts of the industry for help — specifically, they want airports to reconsider their landing charges and fees. But airports are experiencing their own financial cliff, with Airports Council International-North America estimating losses at $8.7 billion.

Last week, Bloomberg reported that White House officials were talking about letting airlines keep ticket taxes or fees that are used to fund airport upgrades, among other things. But airports are sure to fight hard against such a move, and it may not have enough support in Congress.

On Monday, the Air Line Pilots Association, the major union for pilots, wrote to President Donald Trump, House Speaker Nancy Pelosi and Senate Majority Leader Mitch McConnell, saying the group is “unequivocal that any economic relief package must contain strong labor protections.”

And Sara Nelson, the president of the Association of Flight Attendants-CWA, on Twitter called for direct payroll subsidies to flight attendants, pilots, ground workers and caterers, among others.

"Absent payroll subsidies[,] mass layoffs and furloughs are inevitable," Nelson wrote. "This will have long-term consequences because nearly all aviation-related workers have to pass background checks and security and safety training requirements."

Separately, the consultancy the Centre for Aviation has argued that “most airlines in the world” could be bankrupt in less than three months.

“Coordinated government and industry action is needed — now — if catastrophe is to be avoided,” CAPA said, adding that “many airlines have probably already been driven into technical bankruptcy, or are at least substantially in breach of debt covenants.”

Amid the crisis, “the government response has been fragmented — and is being resolved along national lines, with limited consultation,” CAPA said. “As things stand, the likely tepid response to the airline crisis will equally be fragmented and nationally based. It will consist mostly of bailing out selected national airlines. If that is the default position, emerging from the crisis will be like entering a brutal battlefield, littered with casualties.”