When Colleen M. Kelley retires as president of the National Treasury Employees Union, the entire federal workforce, not just her members, will lose a passionate defender against tough attacks.

Kelley, whom Office of Personnel Management Director Katherine Archuleta calls “a strong champion for federal employees,” has announced plans to retire after the union’s August convention.

“We will have the next six months to reminisce about all that we have done together, and to continue to plan the important work of our union,” she said in a message to NTEU chapter presidents. “That work will never be finished.”

After 16 years as president, Kelley is ready to relax, read a stack of books and be with her family in Pittsburgh. That’s her home and where she began her career in federal service as a revenue agent at the Internal Revenue Service.

“I love what I do. I love what NTEU does,” she said in an interview. “I believe we make an incredible difference for our country every day. . . . As long as I’m working, this is all I want to do.”

During her tenure, NTEU membership grew 14 percent, to more than 81,000, while the number of agencies represented increased from 23 to 31.

But at age 63, her working days are almost done and she wants to be at home with her family.

“Isn’t that terrible,” was Sharyn Phillips’s reaction to Kelley’s retirement. But Phillips, a NTEU chief steward in Manhattan, meant it in the kindest way.

Kelley is a “wonderful national president,” said Phillips, who was “shocked” by the news. “We’re going to sorely miss her. I just feel the rug has been taken out from under us.” She sees Kelley as a “role model and hero, someone I’d like to pattern myself after. She’s had that kind of an impact on me.”

The impact Kelley and other labor leaders have had on policies affecting federal employees, however, is less dramatic. Despite Kelley doing “really an outstanding job,” former NTEU president Robert Tobias called the past several years “the most difficult period ever faced by federal employees.”

That period included a three-year freeze on basic pay rates, furloughs, pension hits, verbal and sometimes physical attacks on employees and falling morale. Kelley and colleagues fought back vigorously, but their victories were often defined by what they avoided rather than what they gained.

“She was able to help fight off the worst,” said Rep. Chris Van Hollen (D-Md.), pointing to House Republican budget proposals he said would have been even more “devastating to the welfare and well-being of federal employees.”

Still, much was lost. Kelley’s home agency is an example.

A lot of people might have strong feelings about the nation’s tax collector, but there aren’t many who have Kelley’s positive passion for the IRS. Of her many accomplishments, one of the proudest was the successful fight against the use of private tax collectors. Kelley also has led the charge against congressionally imposed budget cuts that have crippled agency services to taxpayers. Many taxpayers face long holds for phone assistance, if their calls are answered at all. Congressional actions “have been devastating” to the IRS, said Kelley, who is known for her strong command of the issues.

“She got into the nitty-gritty of legislation,” said Rep. Gerald E. Connolly (D-Va.), who called Kelley “a stalwart . . . a passionate advocate for federal employees.”

Even those who were on the other side of the labor-management table have nothing but respect for her.

“I Love Colleen!” John Berry, the previous OPM director and now ambassador to Australia, said by e-mail. “She has been a fierce warrior on behalf of Feds and retirees, and as they say here Down Under, a true Mate! Colleen always had an early alert ‘sixth sense’ for incoming issues, immediate and innovative responses at the ready, and most importantly, through it all, an enormous, big heart, that made her an incredible companion in the trenches.”

Linda Springer, an OPM director during the last Bush administration, which did not have warm relations with federal unions, said, “I always found Colleen more focused on issues than self-promotion, and in Washington that is a noteworthy characteristic.”

NTEU bills itself as “the nation’s largest independent federal-employee union.” That signals its competition with the AFL-CIO’s American Federation of Government Employees, the nation’s largest federal employee union. That rivalry played out in a sometimes rough election campaign to represent 50,000 Transportation Security Administration employees. NTEU lost the 2011 vote, and the relationship between Kelley and former AFGE president John Gage suffered.

But Kelley’s personal and professional relationship with J. David Cox Sr., the current AFGE president, is strong.

Kelley, Cox said, is “one of the best trade unionists I’ve ever come in contact with.”

Twitter: @JoeDavidsonWP

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