Ryanair signed an agreement on Thursday with Belgian cabin crew and pilots to apply local law to their contracts from next year, part of a series of deals aimed at averting further strikes at the airline.

The unions will meet with the Irish company four more times before the end of the year to negotiate agreements on working conditions, including salaries, and may strike again if progress is not made, CNE union representative Yves Lambot said.

"If the negotiations do not advance, obviously we will have to strike again," Lambot said. "But we first have to see what the negotiations bring."

Ryanair has reached similar agreements over the last week with Spanish, Portuguese and UK unions.

"These signed union agreements in Belgium, Spain, Portugal and the UK again demonstrate the considerable progress we're making in concluding union agreements with our people in our major EU markets," Ryanair's Chief People Officer, Eddie Wilson, said in a statement.

Agreements with cabin crew unions in Spain and Portugal will be quickly concluded, Wilson forecast.

The agreements come after months of strikes by Ryanair cabin crew and pilots, after the airline recognised unions for the first time last December.

On Sept. 28, Belgian unions joined workers in five other countries for a 24-hour strike, grounding planes and disrupting the plans of more than 40,000 passengers.

Belgian unions CNE and LBC threatened last week to strike several more times before the end of the year if Ryanair did not change its position.

The agreement on Thursday - to apply Belgian labour law to all pilots and cabin crew based in the country no later than Jan. 31, 2019 - shows progress, Lambot said.

"It shows a change in the attitude of Ryanair, and that is what we wanted," he said.