WASHINGTON (AP) – The AFL-CIO has endorsed Barack Obama for president, uniting the nation’s 15 million union workers behind the presumed Democratic candidate.

The long-expected announcement was made Thursday after an unanimous vote by the labor federation’s 56 unions.

The endorsement by the nation’s largest labor organization was inevitable after Obama’s primary rival, Sen. Hillary Rodham Clinton of New York, endorsed the Illinois senator. The AFL-CIO’s chief rival, the Change to Win labor federation, already has endorsed Obama.

The AFL-CIO already has been campaigning against Republican nominee-in-waiting John McCain. The federation will now use its $200 million in campaign money to also promote Obama’s candidacy to its 10.5 million members.