(Adds no immediate comment from Trump, Biden campaigns)

CHICAGO/WASHINGTON, Oct 27 (Reuters) - The two largest U.S. flight attendant unions, representing more than 75,000 workers, endorsed Democratic candidate Joe Biden on Tuesday ahead of the U.S. presidential election next week.

The unions have been pressing Congress and Republican President Donald Trump to back $25 billion in additional payroll assistance to prevent 32,000 airline furloughs.

The Association of Professional Flight Attendants, representing the 27,000 American Airlines flight attendants, and the Association of Flight Attendants-CWA that represents about 50,000 workers at 20 airlines, said in separate statements they were endorsing Biden.

Asked about the timing of the endorsement, AFA-CWA International President Sara Nelson said: "The complete and total failure of this president on any plan around coronavirus, putting our lives in danger and now putting tens of thousands of us out of work with no hope for fixing that gives us the space to do what we normally would be doing this time of year."

Trump campaign spokesman Ken Farnaso said Biden's "threats to re-close the economy" and said the Democrat's policies would "keep our country grounded and would be the final nail in the coffin for the American travel and hospitality industries."

Biden said this week that he would issue a mandate requiring the use of face coverings in all interstate transportation like airline flights, while the Trump administration has repeatedly rejected mandates. “Right now there's no plan. The only plan is politicizing things like masks which put the people who I represent in more danger not only in terms of their lives, their safety at work, but also the longevity of our industry and our industry's ability to even survive," Nelson said. Airlines and unions had urged action on the new bailout before the prior $25 billion in payroll assistance expired on Sept. 30.

White House Chief of Staff Mark Meadows had said Trump was weighing executive action to avoid massive layoffs at airlines if Congress failed to act, but the White House did not act.

On Oct. 2, U.S. House of Representatives Speaker Nancy Pelosi asked airlines to halt furloughs, saying a long-awaited deal to provide $25 billion to airlines was “imminent."

That deal did not materialize.

Even after the White House endorsed a stand-alone measure to assist airline workers, congressional Republicans and Democrats could not reach agreement on a measure. (Reporting by Tracy Rucinski in Chicago and David Shepardson in Washington; Editing by Rosalba O'Brien and Jonathan Oatis)