Delta Air Lines Inc. would find it easier to block union drives after its merger with Northwest Airlines Corp. under a U.S. labor agency's proposal, a flight attendants group said.

The National Mediation Board plan would bar one organizing tactic, submitting signature cards in favor of representation, and leave elections as the only option, Pat Friend, president of the Association of Flight Attendants-CWA, said this week.

"It looks very suspicious that they are doing it now, because they are going to help Delta destroy collective bargaining rights," Friend said of the NMB in an interview.

The board is taking comments on its proposal as labor groups prepare to organize Delta, the third-largest U.S. carrier, once it buys Northwest later this year. Northwest's major work groups are all in unions while only pilots are represented at Delta, the least-unionized major U.S. airline.

The NMB, a Washington-based federal agency that helps resolve labor disputes, has never let workers use cards alone to gain union membership, unless management backs the effort, Chairman Read Van de Water said this week.

The proposal "is merely stating the practice of the agency for the past 20 years," Van de Water said. "The board has never let authorization cards be used for anything other than an election without carrier agreement."

Delta has no comment on the NMB plan, spokeswoman Betsy Talton said in an e-mail. Delta's all-stock acquisition of Northwest, based in Eagan, Minn., which was announced April 14, would create the world's largest airline.

Attendants at Atlanta-based Delta fell short in May in their second election in six years to join Friend's union. Only 40 percent of the 13,380 eligible attendants voted, and the turnout needed for certification was 50 percent plus one.

Northwest has about 8,500 attendants who are represented by the Association of Flight Attendants-CWA.

A second mediation board move also will stunt organizing, said Ed Wytkind, president of the AFL-CIO's transportation trades department. He cited the NMB plan to require that a union would need to represent "more than a substantial majority" of the combined work group in a merger to extend that status to non-union employees.

"This is a gift to the airline industry, and it's designed to make it much more difficult for workers to retain their collective-bargaining rights," Wytkind said in an interview.

Van de Water said the changes aren't prompted by Delta- Northwest, and the "substantial majority" language wouldn't affect that tie-up. No union besides the pilots would have even a small majority of the combined employee groups, she said.

"This is knee-jerk reaction," she said of union complaints about the proposals. "They think we're out to get them, when we simply wanted their comments and advice."

The board's proposal doesn't define "substantial majority." It now uses a standard of "not comparable" when extending union representation to a merged company with organized employees outnumbering those who aren't. That current standard is also undefined, Van de Water said.

The NMB will take feedback on the proposed changes to its representation manual until early September, and then decide whether to modify or implement them, Van de Water said. The manual provides guidance for NMB staff, labor groups and companies, and isn't binding on the board, she said.

House Transportation and Infrastructure Committee Chairman James Oberstar, a Minnesota Democrat, said he will "strongly consider" legislation to overhaul the board's authority over merger procedures unless the proposals are withdrawn.

Oberstar's comment came in a letter this month to the NMB that was also signed by Sen. Edward Kennedy, D-Mass., and Rep. George Miller, D-Calif.

Harry Hoglander, an NMB member, failed to persuade his two board colleagues to delay consideration of the controversial items until after the Delta merger, according to a letter he wrote this month to Wytkind.

"I believe that this ill-advised action will only strengthen the perception of bias and sow distrust and suspicion," Hoglander said in the letter released by Wytkind.