AirTran Airways and its flight attendants union have reached a tentative agreement on a new labor contract, as they prepare to merge with Southwest Airlines.

The two-year deal, now subject to a ratification vote, includes 4 percent pay increases per year and bonuses ranging from $250 to $4,100 depending on seniority, according to a summary of the deal. Votes will be counted April 18 and the agreement would take effect May 1. AirTran has more than 2,200 flight attendants.

AirTran flight attendants are represented by the Association of Flight Attendants, while Southwest's are represented by the Transport Workers Union.

The Southwest-AirTran deal is expected to bring higher pay to AirTran employees, but it could take a couple of years for those improvements to take effect. The two unions are expected to negotiate how to combine seniority lists and eventually come to an agreement to combine under Southwest.

AirTran and the flight attendants union had been in negotiations for close to three years and reached the deal through mediation guided by the National Mediation Board.

AirTran flight attendants had been picketing at airports around the country and reached the deal the day before they had planned to picket at AirTran's merger approval shareholder meeting Wednesday in Orlando.

AirTran signed a new contract with its pilots last year.