Unions seeking to represent more than 30,000 workers at Delta Air Lines Inc and its Northwest subsidiary could face an uphill battle in elections that could open the door for more collective bargaining and potentially higher labor costs.

The International Association of Machinists and Aerospace Workers and the Association of Flight Attendants-CWA recently asked the National Mediation Board to rule that the 2008 merger of Delta and Northwest Airlines created a single carrier, a move that would require union elections for various workers.

Stakes are high for the unions, which are looking to ensure they have contract-bargaining rights for workers at the world's largest airline.

There's definitely this element of a hurdle because of the fact that the Delta flight attendants have no experience with union representation, said Rene Foss, communications chair at the Northwest flight attendants union.

We believe that we stand to lose a lot if we lose our union representation, Foss said.

The mediation board has the final say, but union officials have said elections could take place later this year. History is not on the unions' side.

Last year, before the Northwest acquisition, only about 40 percent of Delta flight attendants voted to join the AFA. Delta flight attendants also rejected unionization in 2001.

It will be an uphill battle, said Bruce Kaufman, a professor at Georgia State University's Andrew Young School of Policy Studies who specializes in labor economics and human resource management.

Delta has a very progressive human resource program and it has managed over a half-century to keep almost all employee groups from joining a union, Kaufman said.

Kaufman said the labor-management climate at the premerger Northwest was adversarial and contentious, a factor that could lead some Northwest workers to give Delta a chance.

I think the Northwest people are a wildcard but they are going to split, Kaufman said. The majority of the Delta people will still vote for no union, so I think it adds up to no union.

Union victories may lessen Delta's ability to control certain costs as slumping travel demand drains profitability. The Atlanta-based carrier has eliminated thousands of jobs in the past year, and said earlier this month that it would have to cut more salaried positions in the economic slump.

Gary Chaison, a professor of industrial relations at Clark University in Worchester, Mass., said the industry slump could spur more votes for the unions.

I think the (workers') view is that there is more uncertainty with having no union representation in the volatile airline industry and in a partially unionized firm than there is in being unionized, Chaison said in an email.

NORTHWEST UNIONIZED, DELTA NOT

Of the more than 20,000 flight attendants at the combined company, about 7,350 Northwest flight attendants are currently represented by the AFA, while 13,300 Delta attendants are not unionized.

Currently, Delta's only big unionized group is the about 12,000 pilots, who are represented by the Air Line Pilots Association. The carrier has more than 70,000 total workers.

Earlier this month, the machinists union moved to seek elections for baggage handlers and flight simulator technicians, a group that numbers 14,000, according to Delta. About 5,000 of those workers are currently represented by the machinists.

The machinists also represent Northwest stock clerks, ticket and gate agents and office workers. The union said it plans to seek an election for those employees, which total 20,000 at both Delta and Northwest, at a future date.

At a machinists union rally in New York's Times Square this week, airline workers said they feared lower wages and benefit cuts could be in their future should the expected Delta elections be lost.

Delta has a history of union busting, said Robert Roach, general vice president of transportation for the union.

Delta spokeswoman Gina McLaughlin said the machinists union was looking to scare workers and vilify management.

Delta employees have long enjoyed a better package of pay, benefits and work rules when compared to the unions making these accusations, McLaughlin said.

(Additional reporting by Deepa Seetharaman; Editing Bernard Orr)