(Reuters) -Flight attendants at United Airlines voted on Tuesday to reject the tentative agreement for a new contract with the carrier, their union said.

The Association of Flight Attendants-CWA, which represents 28,000 of United's flight attendants, said 92% of the eligible voters cast a ballot, with 71% voting not to ratify the agreement.

The agreement, which the union and United had reached in May, was estimated to result in a financial gain of 40% for the flight attendants in the first year of the new contract.

The president of the United Airlines chapter of the AFA-CWA, Ken Diaz, said on Tuesday that the agreement "didn't go far enough to address" the demands of the flight attendants.

"Our union will survey members as quickly as possible to identify the key issues Flight Attendants are ready to fight to achieve in an agreement they want to ratify," Diaz said.

The union will now return to the negotiations table with United Airlines, until a new agreement is reached.

United's flight attendants, who filed for federal mediation in 2023, are seeking a new contract that includes a double-digit increase in base pay, better compensation for all hours worked - including time on the ground - as well as retroactive pay, more flexible scheduling and improved work rules. They haven't received a pay raise since 2020.