Virgin America (VA) and the Transport Workers Union reached a tentative contract agreement, marking the fourth time in a week that a flight attendants union has announced gains for its members.

Virgin America flight attendants voted to join TWU in August 2014. Once contract talks began it took just 13 months to make a deal, less than half of what might be expected, especially given that the contract is a first for the work group which now numbers about 1,000.

Alaska (ALK) - Get Report and Virgin America await regulatory approval for a merger that was announced in April.

"We wanted to make sure we could improve the quality of life and working conditions for flight attendants," said Thom McDaniel, TWU international vice president.

McDaniel said the two sides were making progress on a tentative agreement when the merger was announced.

"We discussed whether to continue," he said. "We decided we had made such good progress we would finish it out."

The tentative three-year deal includes improvements in compensation, holiday pay and deadhead pay as well as a grievance procedure. McDaniel declined to provide specifics before they are revealed to members.

The deal is contingent upon merger approval. It was important to get a deal, McDaniel said, because once a merger occurs it can be years before joint contracts are negotiated.

The 3,500 Alaska flight attendants are represented by the Association of Flight Attendants. Given the higher membership, it is likely that AFA will represent flight attendants at the merged airline.

"I want every flight attendant to have a good union and to be protected by a good contract," McDaniel said. "The Alaska contract is very good."

Virgin America spokesman Dave Arnold called the agreement "a testament to the hard work, diligence and commitment of the negotiation committee of the TWU and Virgin America representatives.

"If ratified, this agreement will provide important improvements to compensation and work rules as well as a defined path forward for their integration with Alaska Airlines, pending regulatory approval and merger close, which we still anticipate will occur in the fourth quarter of this year," he said.

Last week, unionized U.S. flight attendants gained ground at United, Allegiant and Norwegian Air Shuttle.

United's 25,000 flight attendants, represented by AFA, ratified a joint contract six years after the merger between United and Continental. Allegiant and the TWU reached a tentative agreement on the first contract ever for the airline's 1,000 flight attendants.

And the Norwegian Cabin Crew Association won an election enabling it to represent the carrier's U.S.-based flight attendants. The group is expected to number about 500 by year-end.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.