U.S. airlines were awaiting progress on COVID-19 relief proposals in Washington that could include another $17 billion in payroll support for an industry bracing for a renewed slump in air travel as cases spike across the country.

The number of passengers screened at U.S. airports dipped to 501,513 on Tuesday, the lowest number since July 4 as COVID-19 cases spike, and Delta Air Lines' chief executive warned that the outlook remained bleak in the months ahead.

An initial $25 billion in payroll support for airline employees expired in October, prompting tens of thousands of furloughs.

Airlines have lobbied for fresh relief, arguing their infrastructure is critical to quickly and widely distributing COVID-19 vaccines.

A summary of the draft legislation seen by Reuters would provide payroll aid through the end of March, protecting workers and banning share buybacks and dividends and limiting executive compensation during that period.

U.S. carriers are burning $180 million in cash every day, with passenger volumes down 65% to 70% and cancellations rising, industry lobby Airlines for America (A4A) said on Wednesday.

Speaking on CNBC, Delta CEO Ed Bastian said he does not see the trend changing for the next couple of months.

However, he said there is "enormous pent-up demand" for spring travel, when there is a possibility that tens of millions of Americans will have been vaccinated and "ready to get on with their lives."

The Transportation Security Administration (TSA), which releases daily passenger screenings at U.S. airports, said traffic on Tuesday was down about 74% from the same weekday last year when it screened 1.9 million people.

Several airlines in recent days have reported a softening in passenger demand as U.S. health officials advise against holiday travel. On Monday, the TSA screened 703,546 people.

Separately Airlines for America said it had elected Southwest Airlines CEO Gary Kelly as chairman of the board for a two-year term.