The Senate is poised to spend most of this week debating the Employment Non-Discrimination Act. Here's everything you need to know about the bill:

What is ENDA?

The Employment Non-Discrimination Act would ban employers from firing, refusing to hire or discriminating against workers or job applicants based on their sexual orientation or gender identity.

The ban would join similar federal workplace protections based on race, religion, gender, age and disability.

If the bill is ever passed, potential remedies for violating the law would be on par with other cases of employment discrimination. The worker would get the job or promotion they were denied; be awarded back pay and litigation costs and/or related compensatory or punitive damages.

How many gay and lesbian workers are there nationwide?

There are roughly 8.2 million gay and lesbian employees nationwide, according to estimates released by the Williams Institute at UCLA. Researchers at the nonpartisan think tank study gay rights in public policy and drew their estimate from U.S. Census data on the public- and private-sector workforce.

A Pew analysis of Census data also found that same-sex couples are more apt to have both partners working (58 percent) than opposite-sex married couples (47 percent) and opposite-sex unmarried couples (55 percent).

But wait -- I thought it was already illegal to discriminate against gay and transgender workers. Isn’t it?

Not everywhere.

Currently 21 states and the District of Columbia have laws prohibiting workplace discrimination based on sexual orientation. Seventeen states and the District also bar discrimination based on sexual identity. Maryland passed a law prohibiting discrimination based on sexual orientation in 2001; Virginia has no laws regarding sexual orientation or gender identity on the books.

What do Americans think of this issue?

A little more than seven in 10 Americans favor protecting gay men and lesbians from job discrimination, according to a May poll by the Public Religion Research Institute.

Public support has been generally consistent for years. A Time/CNN poll from 1994 found that 62 percent of Americans said they favored passing “equal rights laws” to protect “homosexuals” against job discrimination.

Seven in 10 Americans believe that gays and lesbians face “a lot” or “some discrimination” at the office, according to a Pew Research Center poll from May. Those figures are greater than the number who perceived discrimination against African Americans, Hispanics, and women, but on par with perceived discrimination against Muslims.

So then why hasn’t Congress addressed this already?

Supporters have been trying since 1994, when Rep. Gerry Studds (D-Mass.) and Sen. Edward M. Kennedy (D-Mass.) first introduced the legislation. But their efforts faltered in House and Senate committees. Supporters tried again in 1995, 1996, 1997 and 1999 and failed repeatedly.

In 2001, Kennedy succeeded in bringing the bill to the full Senate, but it did not pass. Supporters led by Rep. Barney Frank (D-Mass.) succeeded in getting the bill passed by the Democratic-controlled House in 2007, but the bill failed again in the Senate.

The most recent version of ENDA cleared the Senate Health, Education, Labor and Pensions Committee with bipartisan support in July. A House version has yet to be considered by GOP-controlled committees.

Why do most Republican lawmakers oppose ENDA?

They generally believe that the law is unnecessary because federal statutes already prohibit workplace discrimination and many private companies already have policies banning the practice. They also worry that ENDA is written too broadly and would cause greater legal risk for employers who are perceived to be discriminating against gay, lesbian and transgender employees or job applicants.

But a recent Government Accountability Office report found that states with laws similar to ENDA have not seen a noticeable increase in litigation based on sexual orientation or gender identity.

So will Congress pass ENDA this time?

The Senate is expected to pass the latest version of ENDA as early as this week with the support of all members of the Senate Democratic caucus and at least five Republicans.

But the office of House Speaker John A. Boehner (R-Ohio) said Monday that he believes the legislation would “increase frivolous litigation and cost American jobs, especially small business jobs" and will not bring up the bill for consideration.

In response, House Minority Leader Nancy Pelosi (D-Calif.) told MSNBC over the weekend that she hopes that President Obama, congressional Democrats and outside groups can work together to put pressure on House GOP leaders to hold a vote. If forced to hold a vote, Pelosi predicted that Boehner would need to rely on a handful of Republicans and a majority of Democrats to pass the bill.

Peyton Craighill and Scott Clement contributed to this report.

Learn more about ENDA and its political fate on Capitol Hill by watching this video:

The Senate this week will debate the first major gay rights legislation since Congress voted to repeal the military’s “don’t ask, don’t tell” in late 2010. Congressional reporter Ed O'Keefe tells us what to watch for in the discussion surrounding the Employee Non-Discrimination Act. (The Washington Post)