"I'm convinced that Senator Obama's message of hope and 'change we can believe in' has resonated across our country," said Cohen, whose union will not endorse until June.
Those endorsements, including recent ones by the International Federation of Professional and Technical Engineers and the American Federation of Government Employees, are helping Obama cement his front-runner status against Hillary Rodham Clinton.
Obama supporters hope his union endorsers will help bring in the white, blue-collar Democrats his campaign has been courting. The Service Employees International Union, the nation's largest, is already calling Obama "the presumptive nominee."
But there is still a major union plum to be had, the AFL-CIO, the nation's largest labor organization.
The AFL-CIO and its 56 unions expect to spend an estimated $200 million on the presidential and congressional elections. However, the labor federation is still nowhere close to making an endorsement, focusing its energies instead on presumptive Republican nominee John McCain.
To win its formal backing, a candidate must have support from two-thirds of the union's 10 million members.
Including the Steelworkers, Obama has been endorsed by nine AFL-CIO unions and four unions from Change to Win, a rival labor organization.
Clinton still has more union support, having been endorsed by 13 AFL-CIO unions and Change to Win's United Farm Workers.
Obama started the year with no major union support, but his rise in popularity among unions may be causing restlessness among some of Clinton's union supporters. Her key union backers — the American Federation of State, County and Municipal Employees, the American Federation of Teachers and the International Association of Machinists and Aerospace Workers — all say they will not abandon her despite the slim odds of her becoming the nominee.
But everyone inside those unions may not be on the same page.
AFSCME President Gerald McEntee said in an interview that he and the national union will continue to support Clinton no matter what. "We just believe Obama has a higher mountain to climb than Clinton to beat McCain," McEntee said.
That puts the Washington leadership in direct conflict with its members in Oregon, which holds a presidential primary next Tuesday.
Oregon's AFSCME Council 75 endorsed Obama — locals are allowed to endorse separately from the parent union — and said it asked McEntee and those who do not support Obama to not campaign in Oregon.
Council 75 Executive Director Ken Allen told his members last week the union was sending letters to Oregon members asking them to vote for Clinton anyway.
"McEntee's actions are disrespectful to our Oregon leaders, members and a waste of money. Given the status of the race at this time his efforts are probably meaningless," Allen said in a letter to his members.
Allen said they will try to change the union's endorsement process at AFSCME's national convention later this year.
Obama's major union supporter, the SEIU, also is facing some strife and possibly picket lines at its June convention in Puerto Rico, where Obama is expected to speak.
The union is facing criticism on several fronts, including from Sal Rosselli, leader of United Healthcare Workers West, one of SEIU's largest locals. Rosselli has accused union president Andy Stern of a "growth at any cost" strategy, and of making deals with companies at the expense of higher contract standards. Stern and his allies counter that short-term sacrifices at the bargaining table will yield membership gains — and more clout in the long run.
In addition, the California Nurses Association, an AFL-CIO member, and the SEIU are competing to sign up nurses. SEIU complains that the California organization is raiding its members, and the debate turned physical in April when union members scuffled at a labor conference in Michigan.
Stern said the issues being debated are important, but SEIU is focused on organizing workers and electing Obama.
"We have an opportunity to elect a pro-worker president, bring health care coverage to the 50 million people who don't have it, and change the laws to guarantee all workers the freedom to form a union," he said.