Sen. Barack Obama stressed his record as a champion of workers' rights at a union forum on Tuesday that also attracted fellow Democratic White House hopefuls John Edwards and Hillary Clinton.

"I am confident in my ability to lead," Obama told members of the Communication Workers of America.

The top Democratic contenders for the White House worked to impress the crowd about their pro-labor credentials, support for universal health care coverage and calls for an end to the war in Iraq.

Answering charges that he is more style over substance, Obama pushed his record as a state legislator, community organizer and academic background as a professor and argued that he has the gravitas to be president.

He also said the nation needs to make better choices so it isn't "competitive on the backs of workers." The nation's health care system is broken, Obama added, and education is suffering under President Bush's policies.

He referred to the Bush administration's view of the world and workers as "social Darwinism" and delivered a harsh rebuke to what he termed the president's "ownership society."

A member of the audience interrupted Obama by yelling out "Throw the bums out" to which Obama responded, "We have already thrown some of the bums out ... but we don't want new ones coming in."

The CWA's powerful endorsement could bring in lots of campaign cash. The group, which endorsed Democratic presidential nominee John Kerry in 2004, is the largest telecommunications union in the nation with 700,000 members. It has said it will withhold its endorsement for the time being as it hears from the candidates.

The union supports the Employee Free Choice Act, which would simplify the process of forming and joining unions and increase penalties for violations of employee rights. All the 2008 contenders stressed their support for the act.

Edwards, a former Democratic senator from North Carolina and Kerry's running mate in 2004, also offered his credentials on other pet issues of the union such as increased broadband access and the need for a ban on hiring permanent replacements for striking workers. Edwards said he was the first Democrat with a "truly comprehensive" health care plan.

"We need big, bold change in America," Edwards said.

Sending regards from his wife, Elizabeth, who revealed last week that cancer has spread to her bones, Edwards quipped that as a result of all the news coverage about her, she told him, "I am sick of me."
He also carried the populist message, calling global warming an "emergency" and he criticized "Bush and his gang" for taking money away from education.
"This country, we are so much better then we are acting," Edwards said about global warming. "It is time for us to be patriotic with something other than war. ... We need big, bold change in America."

Clinton, the Democrat senator from New York, also vowed her support for the union's issues, saying in contrast to Bush, "you're not invisible to us, not to this union and not to me."

"When I'm sworn into president and I'm hearing of all these big holes ... that have been dug over the last six years, I'm going to have everybody in America shoveling. We are going to start digging our way out," Clinton said.

About 20 minutes before Clinton's speech, five Code Pink protesters were asked to leave the hotel and threatened with arrest. CWA spokespeople said the protesters were intending to interrupt Clinton, though the protesters who had been standing there for two hours, denied that to FOX News. CWA Secretary-Treasurer Barbara Easterling took the microphone and told the audience, "The group that was here, they disrupted, and we don't need that to be the focus of the conference. ... We are here to do a job and we don't need anyone to disrupt that."

FOX News' Mosheh Oinounou and The Associated Press contributed to this report.