CHICAGO -- U.S. Sen. Barack Obama pledged Saturday that the Senate would pass a bill making it easier for workers to start unions against companies' wishes, but acknowledged it won't be easy to get it past the Bush White House.

"We may have to wait for the next president to sign it, but we will pass it," the Democratic presidential candidate told a cheering crowd of more than 1,000 people at a Chicago labor rally. "We will get this thing done."

It may not be that easy. The Senate's Republican leader has said he will block the measure and the White House says President Bush will veto it if it gets to his desk.

The Employee Free Choice Act passed the House on Thursday.

Obama headlined the rally that included national and local labor leaders, along with fellow Illinois Sen. Dick Durbin and U.S. Rep. Jan Schakowsky. The event was sponsored by the American Federation of State, County and Municipal Employees Council 31, which has 100,000 active and retired members in Illinois.

It was Obama's second major public appearance in his hometown in as many days, although the state's junior senator did not take questions from reporters at either event.

On Friday, Obama gave a foreign policy address here to the American Israel Public Affairs Committee, where he emphasized his commitment to the security of Israel and castigated the Bush administration for failings in Iraq that he says have strengthened the strategic position of Iran.

From Chicago, Obama was headed to Selma, Ala., to commemorate on Sunday the 42nd anniversary of the civil rights march that helped end segregation in the South.

Fellow Senator and Democratic revival Hillary Rodham Clinton is also scheduled to be in Alabama as the two work to lock up a crucial bloc of Democratic voters.

People at the Chicago labor rally said they were pleased Obama made time in his schedule to attend their event, which was also held to show support for union organizing at a local health care system.

Correctional worker Leonardo Corbett said Obama's presence sends a message to employers and will help union organizing efforts.

Corbett said it's a real plus "to have somebody with this amount of national popularity come and support us."

NBC5's Lauren Jiggetts reported that Obama was undoubtedly the main attraction at the rally, which was sponsored by the American Federation of State, County and Municipal Employees.

The focus was making it easier for workers to organize, but some of those who turned were there to rally around the charismatic candidate for president.

Anti-war protestors briefly interrupted Obama's speech. And as he left, it was near chaos as his supporters followed him all the way to the door of the Hyatt Regency Chicago.

On Sunday, Obama travels to Selma, Ala., where he'll mark the 42nd anniversary of the Civil Rights Movement's Bloody Sunday by taking part in a march along with another presidential hopeful, Sen. Hillary Clinton.