Update at 6:47 p.m. Senate Passes Bill:

With a vote of 61-30, the Senate voted to move forward on legislation that would prohibit workplace discrimination on the basis of sexual orientation and gender identity.

The vote Monday opens the floor to debate on the bill and the Senate is expected to schedule a full vote by week's end.

Our original post continues:

The Senate is expected to vote Monday evening for cloture on the Employment Non-Discrimination Act (ENDA), a bill that would forbid employers with at least 15 employees from discriminating on the basis of sexual orientation and gender identity.

The measure, which has been around in various forms for decades, has more Senate support than ever before — but likely not enough in the GOP-controlled House to become law.

Politico reported Monday that House Speaker John Boehner opposes the legislation, and believes it would cost jobs and lead to frivolous lawsuits.

So far, every Democratic senator and both independents have said they will vote for the bill this year. And there are two Republican co-sponsors, Sen. Susan Collins, R-Maine, and Sen. Mark Kirk, R-Ill.

Still, at least five Senate Republicans will have to support ENDA to defeat a filibuster.

Two Republicans — Orrin Hatch of Utah and Lisa Murkowski of Alaska — are also expected to support ENDA, although neither has officially stated they will. Both voted for the Senate bill in its current form this summer, when it passed the Senate Health, Education, Labor and Pensions Committee.

On Monday, Republican Dean Heller of Nevada added his support for the bill. "After listening to Nevadans' concerns about this issue from a variety of viewpoints and after numerous conversations with my colleagues, I feel that supporting this legislation is the right thing to do," Heller said in a statement.

That puts the tentative vote count at 60, just enough to defeat a filibuster. The bill's advocates hope even more Republicans will throw their support behind the legislation, which they believe would send a strong message of bipartisan support for LGBT protections.

Fred Sainz, the vice president of communications and marketing at the Human Rights Campaign, says the organization has focused its efforts on getting support from Heller and Sens. Kelly Ayotte, R-N.H., Pat Toomey, R-Pa., and Rob Portman, R-Ohio.

"We are cautiously optimistic that we'll be there [on Monday], but we're not taking anything for granted," says Sainz. "Nothing is sure until the vote takes place."

Sainz says organizers in seven states have held 150 events to garner grass-roots support for ENDA. So far, these events have generated over 200,000 constituent contacts to these prospective senators in support of the bill. Supporters of the legislation have been targeting Portman, in particular, who came out in support of same-sex marriage earlier this year.

Caitlin Dunn, Portman's press secretary, said in an email that the senator "agrees with the underlying principle of ENDA and supports ending unjust discrimination based on one's sexual orientation. He doesn't think one of his constituents should be able to be fired just because he or she is gay. The bill as it stands, however, is not perfect, and he continues to discuss his concerns with the bill's sponsors and is exploring ways to strengthen the bill, including its religious liberties provisions."

The last time ENDA faced a vote in the Senate was in 1996, when Republicans held the majority. It failed with a final vote of 49-50.

Currently, 29 states have no legislation banning employment discrimination on the basis of sexual orientation, and 33 states are without gender identity employment protections.

Federal employment protections that prohibit discrimination on the basis of race, color, religion, sex, national origin, age, disability and genetic information are already in place.

If the Senate votes for cloture on the bill Monday, a final vote is expected on Wednesday.

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