(Reuters) - Southwest Airlines ( LUV ) said on Wednesday it has reached a tentative agreement, including for better wages, with its flight attendants' union in a new contract covering nearly 20,000 cabin crew members.

The airline's flight attendants had been demanding higher pay and better work rules. The previous contract came up for renewal in 2018.

In the past two years, unions across the aerospace, construction, airline and rail industries have demanded higher wages and more benefits in a tight labor market.

The tentative agreement, which will need to be ratified by workers, marks a third attempt by the largest U.S. domestic carrier to get into a deal with its flight attendants.

Cabin crew members had approved a strike mandate in January after rejecting a second tentative contract, which proposed a 20% pay raise for 2024 and a 3% annual raise in 2025, 2026, 2027 and 2028.

The details of the latest agreement were not disclosed. The Transport Workers Union's local chapter, representing the flight attendants, will present details of the deal - for which the voting will begin in a few weeks - directly to the cabin crew members.

"Our membership is the ultimate authority (on the agreement)," TWU Local 556 President Lyn Montgomery said.

Cabin crews at carriers in Canada and the United States have been demanding to be paid for more of their hours at work - a fundamental change from how the industry currently compensates them by paying largely only when the aircraft is in motion.

Bumper pilot contracts have driven up operating costs across major airlines and have also encouraged other groups to demand similar gains.

Southwest's ( LUV ) rivals American Airlines and United Airlines are also in negotiations with their flight attendants.

Southwest ( LUV ) has ratified contracts with nine worker groups since October 2022. Earlier this year, it reached a new deal with its pilots, which will offer about a 50% pay raise over a five-year period.