The union said the move followed its discovery that a number of authorization cards submitted by workers "contain insufficient information or questionable signatures." It intends to resume organizing and refile for an authorization vote in 12 months.

The IAM filed for an election in January, saying it had about 12,000 authorization cards representing 60 percent of Delta's 20,000 flight attendants.

On Monday, the union said in a statement that the "number of questionable cards makes our showing of interest borderline."

Withdrawing the application starts a 12-month waiting period before the union can file for another election, the union said.

That track is faster than waiting several months for the NMB to make a determination, then starting the 12-month clock, the union said.

In a notice to employees, Delta said the union's statements "appear to validate the many concerns raised by many of you when the IAM filed for the election."

The IAM also is seeking to organize workers at Boeing Co facilities in South Carolina and Airbus Group NV facilities in Alabama. A vote by Boeing workers is set for April 22.

(Reporting by Alwyn Scott; Editing by Jonathan Oatis and David Gregorio)