As many as 10,000 hotel workers were on strike across the United States on Sunday, at the height of a long holiday weekend in which millions of Americans were expected to travel.

Strikes were launched at 25 hotels in eight cities including Boston, San Francisco and Honolulu, as workers demand improved pay and a return to pre-Coronavirus staffing levels.

Hotels from the Hilton, Hyatt and Sheraton chains were affected with 5,000 workers walking out in the Hawaiian capital Honolulu alone, affecting 10,557 rooms there, according to the UNITE HERE union which called the strikes.

The union said in a statement "that many hotels took advantage of the Covid-19 pandemic to cut staffing and guest services that were never restored, causing workers to lose jobs and income."

Strikers were manning picket lines at several hotels in Boston, an AFP correspondent saw, while a rally was planned for Monday.

"Now the hotel industry is making record profits while workers and guests are left behind. Too many hotels still haven't restored standard services that guests deserve, like automatic daily housekeeping and room service," added the union's international president Gwen Mills.

"Workers aren't making enough to support their families."

Hyatt said in a statement it was "disappointed that UNITE HERE has chosen to strike while Hyatt remains willing to negotiate.

It said it had "contingency plans in place to minimize impact on hotel operations."

According to booking data from the motoring group AAA, overall domestic travel over the Labor Day holiday weekend is up 9 percent compared to last year.

As many as 17 million passengers were planning to fly through Wednesday, the US Transportation Security Administration said in a statement.

Hilton and Marriott did not respond to requests for comment.