Delta Air Lines flight attendants chose to remain non-union in a vote that concluded Wednesday.

In the vote on whether to join the Association of Flight Attendants-CWA union, 5,253 of 13,380 eligible voters cast "yes" ballots, well short of the majority required, the National Mediation Board said. Employees who don't vote are counted as "no" votes. A total of 5,306 ballots were cast.

It was the second time in this decade that a flight attendant union drive failed. An earlier drive was defeated in 2002.

But the latest vote comes as Atlanta-based Delta works toward a planned merger with Northwest Airlines, which brings some uncertainty for the airline's employees.

The AFA represents more than 55,000 flight attendants at 20 other airlines. Because Northwest's roughly 8,000 flight attendants are already represented by the AFA, the National Mediation Board is expected to schedule a second election after the merger where flight attendants of the combined carrier would vote on whether to be represented by the AFA. That election is expected to happen in early 2009.

Delta's only major group of unionized employees is the Air Line Pilots Association at Delta representing more than 7,000 pilots.

The AFA said a campaign by Delta management discouraged flight attendants from voting. The AFA also said it plans to file interference charges with the National Mediation Board by June 6.