Delta Air Lines Inc ticket and gate agents have voted to reject union representation, dealing another blow to labor groups seeking to represent a majority of workers at the carrier.

The International Association of Machinists and Aerospace Workers (IAM), which was seeking to represent the customer service agents, also failed to get a majority vote for unionizing among Delta baggage handlers and TechOps Stores workers last month.

The Association of Flight Attendants-CWA (AFA) also lost its bid to represent 20,000 Delta flight attendants in November.

Elections for Delta work groups that include about 50,000 employees took place this fall to resolve labor representation after the 2008 acquisition of mostly unionized Northwest Airlines by Delta, the least unionized of major U.S. airlines.

The union losses bolster Delta in its bid to remain largely union-free. But they handed setbacks to labor unions which were

hoping to make gains in wake of a U.S. law change that was believed to enhance their chances of winning.

It doesn't matter what the rules are, said Mike Campbell, Delta executive vice president for human resources and labor relations, during a reporter briefing. Our people are saying they don't want to be represented by the IAM or the AFA.

The National Mediation Board said on Tuesday that of 12,518 valid votes cast from Delta passenger service employees, which include gate and ticket agents, customer-facing cargo agents and reservation sales workers, 3,772 favored unionization. That includes 3,638 votes for the machinists, while 8,746 chose no union. There were 15,436 employees eligible to vote.

Under the change in federal labor law that took effect this year, the outcome of union elections at airlines and rail companies is now based on votes cast. The previous rule required a majority of an entire work group to approve unionization, effectively counting those who did not vote as no votes. Unions supported the rule change.

Delta said the ticket and gate agents were the ninth group of workers at the carrier to resolve union issues since the Northwest merger.

For those Northwest workers who were unionized before the vote, dues are no longer withheld, Campbell said.

MACHINISTS PLAN INTERFERENCE CHARGES

Still, the unions have charged that Delta interfered in the election process. Such claims, if found to be valid, could delay Delta's effort to fully align pay and work rules of the pre-merger Northwest and Delta workers.

On balance, the pay of Delta employees was generally better than that of Northwest employees, Campbell said.

The Association of Flight Attendants-CWA filed formal interference claims with the National Mediation Board last month. It alleged that Delta management used coercive methods to influence the election, including inundating staffers with messages urging them how to vote.

The machinists union on Tuesday said it planned to present evidence of Delta interference in the baggage handler and TechOps Stores votes this week, and added it would also file interference charges in the just-ended customer service agent election.

Campbell said Delta had until late December to respond to the AFA interference charges, and he added that there was no set timeframe for the National Mediation Board to review the matter.

(Reporting by Karen Jacobs)