Flight attendants at US Airways Group rejected a tentative agreement offered by management, and union leaders said the members want a better financial offer.
Leaders of the Association of Flight Attendants union called for "substantial improvements to our current contracts" in a statement on the results on Friday.
The vote was 1,457 in favor of ratification and 4,375 against, the joint negotiating committee for the flight attendants at US Airways said in a website update.
The present US Airways was formed from a 2005 merger with America West Airlines. The flight attendants from the former US Airways and America West have been working under separate contracts.
US Airways is exploring a potential merger with bankrupt American Airlines.
"We are obviously disappointed that our flight attendants chose to vote against ratification of a new contract," Doug Parker, US Airways' Chairman and CEO, said in a statement.
He added the tentative agreement that would cover 6,700 flight attendants, reached in January, came after years of negotiations and was achieved with help from the U.S. National Mediation Board.
"We will now consult with the NMB and AFA leadership to determine the best steps going forward to one day reach a ratified agreement," Parker said.
(Reporting by Karen Jacobs; Editing by Gary Hill)