Delta Air Lines customer service agents overwhelmingly voted against unionization Tuesday, the latest blow to unions at the former Northwest Airlines.

Unions seeking to represent all of Delta's flight attendants, baggage handlers and technical operations workers have lost a series of votes this year, representing 56,000 Delta workers. Delta, the least unionized of the major U.S. airlines, said it would now be able to align the pay and benefits of former Northwest employees with those of longtime Delta workers.

Tuesday's vote, with 8,746 votes against the union to 3,772 in favor of it, nullifies the union contract for the International Association of Machinists and Aerospace Workers (IAM), which had represented former Northwest workers. About 81 percent of eligible workers voted.

Like the other rejected unions, the IAM accused Delta of "illegal interference" in Tuesday's union election, and said it plans to file charges to that effect with the National Mediation Board in Washington. A union representative did not return a call for comment.

The Association of Flight Attendants-CWA last month filed interference claims with the National Mediation Board in connection with its union election at Delta. The IAM also said it would present evidence that Delta interfered in other union elections.

Earlier this year, the board held that Delta had interfered with a union election involving flight simulator technicians, the IAM said. Delta said the National Mediation Board had found it in violation on only two of several interference complaints in that election.

The anti-union votes were aided by the fact that, in most cases, non-unionized Delta workers heavily outnumbered unionized former Northwest employees. In Tuesday's vote, non-union employee voters outnumbered union workers by more than two to one.

Tuesday's defeat came even though federal voting rules for union organizing efforts had been changed in the unions' favor. Instead of having to win a majority of all union members eligible to vote, a union had to win only a majority of those who actually voted. As a result, stay-at-home voters were no longer counted as "no" votes.

"People have made their choice and they have made it loud," said Mike Campbell, Delta's executive vice president of human resources and labor relations, during a conference call with reporters. "It's time to respect their decision."

The Atlanta-based carrier does have two unions: the Air Line Pilots Association and the Professional Airline Flight Control Association, both of which existed before the Northwest merger.

The voting is "a major blow to organized labor," said John Budd, head of the Center for Human Resources and Labor Studies at the University of Minnesota's Carlson School of Management. Over several decades, "increases in union membership have failed to keep pace with the growth of new jobs. But rarely has the labor movement lost so many union members" at once, as it did with the former Northwest workers.

All the unions faced an uphill battle at Delta because of "the numerical superiority of the nonunion Delta employee groups," Budd said.

Others agree.

"I don't think this is the death knell for unions, but it reflects a trend of unions having a much more difficult time winning elections these days," said Marshall Tanick, an employment and labor attorney at Mansfield, Tanick & Cohen in Minneapolis. Unions are having trouble getting a foot in the door because employers are offering better compensation packages, workers are less personally involved with co-workers and there is fear among workers that unionization might bring a loss of jobs, he said.

"From a Delta management standpoint, you have to consider this a significant victory, because they don't have to deal with many unions," Tanick said. "From a working conditions standpoint, time will tell. And how it affects passengers remains to be seen. Will they get good treatment from Delta workers, or will Delta employees be less service-oriented?"

Others were more confident about Delta's future.

Delta avoided further unionization because "it treats its people well and fairly" on important issues such as pay, working conditions, quality of life and benefits, said Jerry Glass, president of F&H Solutions Group, a management, labor relations and human resources consulting firm in Washington.

"This won't change anything for Delta," Glass said. "Prior to the Northwest acquisition, they had two unions. And now that all the union elections are done, Delta still has two unions."

Regardless of what the mediation board decides, more union votes could be in Delta's near future.

"The elections among flight attendants and fleet service employees were quite close," Budd said. "So it would not be surprising to see continued attempts to unionize these groups in future years."

Steve Alexander • 612-673-4553