WASHINGTON (AP) - Invoking the Declaration of Independence, proponents of a bill that would outlaw discrimination against gays in the workplace argued on Tuesday that the measure is rooted in fundamental fairness for all Americans. Republican opponents of the measure were largely silent, neither addressing the issue on the second day of Senate debate nor commenting unless asked. Written statements from some rendered their judgment that the bill would result in costly, frivolous lawsuits and mandate federal law based on sexuality. The Senate moved closer to completing its work on the Employment Non-Discrimination Act that would prohibit workplace discrimination against gay, bisexual and transgender Americans. Senate Majority Leader Harry Reid, D-Nev., said a final vote in the Senate is possible by week's end. Senate passage of the bill would represent a major victory for advocates of gay rights just months after the Supreme Court affirmed gay marriage and granted federal benefits to legally married same-sex couples and three years after Congress ended the ban on gays serving openly in the military. Illinois was poised to become the 15th state to legalize gay marriage after the state's Legislature gave its final approval Tuesday, sending it to the governor, who has said he'll sign it. "I don't believe in discriminating against anybody," said Sen. Orrin Hatch, R-Utah, a backer of the measure who voted against a similar, narrower bill 17 years ago. Hatch said the bill has language ensuring religious freedom that he expects the Senate to toughen. The measure, however, faces strong opposition in the Republican-controlled House, where Speaker John Boehner, R-Ohio, maintains that it is unnecessary and could prove too expensive and litigious for businesses. Resistance remains within GOP ranks even as the national party, looking beyond core older voters, tries to be more inclusive. Republicans struggled to win over young people and independents in the 2012 presidential election. Asked why he opposed the bill, Sen. Jim Inhofe, R-Okla., said the measure is "somewhat pandering to the special groups that I think should not have to be singled out by themselves. I think they're normal citizens like everybody else. A bipartisan group of senators pressed ahead with the legislation, casting it as a clear sign of Americans' greater acceptance of homosexuality that has significantly changed the political dynamic. A Pew Research survey in June found that more Americans said homosexuality should be accepted rather than discouraged by society by a margin of 60 percent to 31 percent. "What changed is society has changed," said Sen. Tom Harkin, D-Iowa. Personal attitudes have changed, business is for it. There's just widespread support for taking these other steps in passing a civil rights bill. A chief sponsor of the measure, Sen. Jeff Merkley, D-Ore., said that in his home state, Nike supports the measure. "It's time to end this discrimination," Merkley said in a Senate speech. It's certainly about the vision of the Declaration of Independence that has the promise of life, liberty and pursuit of happiness as the founding motivation. Democratic Sen. Chris Murphy said his home state of Connecticut has had a discrimination law since 1991 and frivolous lawsuits are uncommon. Based on the latest data from 2009 and 2010, 53 of 1,740 employment-based complaints were based on sexual orientation, Murphy said. "Fifty years from now history is going to judge no less harshly those that voted against this act as it judges now those that voted against some of the civil rights acts of the 1950s and 1960s," Murphy said. Sens. Rob Portman, R-Ohio, and Kelly Ayotte, R-N.H., were crafting an amendment to the bill that would prevent federal, state and local governments from retaliating against religious groups that are exempt from the law. "It focuses on religious liberty," Portman said. It provides a non-retaliation clause in the federal law comparable to what a lot of states have. Sen. Pat Toomey, R-Pa., was working on an amendment to expand the number of groups that are covered under the religious exemption. Portman, Ayotte and Toomey were the last three Republicans who voted Monday night to advance the bill as it past its first hurdle on a 61-30 vote. After the vote, Portman's son Will, a student at Yale, tweeted, "Go dad ... Sens Portman and Toomey vote yes. Cloture is reached on #ENDA. The Ohio senator announced in March that he supports same-sex marriage, saying his views began changing in 2011, when his son told his parents he was gay and that it wasn't a choice but "part of who he was." Portman said he exchanged messages with his son after the vote.