CHICAGO ( TheStreet) -- The battle to represent flight attendants at the new United ( UAL) has begun.

The Association of Flight Attendants, which represents about 15,000 United flight attendants, planned to file with the National Mediation Board to declare that United is a single carrier, which would trigger a union election.

The International Association of Machinists, which represents 9,500 Continental flight attendants, said it is too soon to declare a single carrier because United and Continental are not yet operating as one.

An election would determine which of the two unions would represent the combined group at the merged airline. Between them, Continental and United have eight categories of workers who fall into 13 unionized work groups. Among the eight groups, pilots and mechanics are represented by the same union at both carriers, but elections will be required among most of the other groups, the largest of which are flight attendants and ramp workers.

"Management must know that the flight attendant workforce is unified, and that we expect the best flight attendant contract at the world's leading airline," said Greg Davidowitch, AFA United President, in a prepared statement. "Joined together in AFA, we can ensure flight attendants are full partners in the merger with compensation that reflects our key role in the success of the new United Airlines."

But IAM spokesman Joe Tiberi said, "We think it's premature to file at this point. We believe flight attendants should have time to learn about both unions before they make a decision on representation."

Tiberi said flight attendants at Continental are about to vote on a new contract that offers higher salaries and more flexibility than United flight attendants have, as well as job guarantees in a merger.

"We have improved what was already the best-paying legacy contract in the industry," he said.

The United flight attendant contract is a concessionary one, signed during the carrier's bankruptcy, but a new contract is currently being negotiated.

The AFA is the country's largest flight attendants union and has long played a role in improving working conditions for flight attendants. The IAM is the largest union in the airline industry and the largest at United, where it represents three work groups.

Both unions are focused on United after losing bids to unionize workers at Delta ( DAL) following its merger with Northwest. The results are being appealed, but the losses, if they are sustained, would be a blow to the unions, resulting in the loss of thousands of members whom they represented at Northwest.

-- Written by Ted Reed in Charlotte, N.C. .

>To contact the writer of this article, click here: Ted Reed