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.
How many gay workers are there nationwide?
About 8.2 million, according to estimates released by the Williams Institute at the University of California at Los Angeles. The nonpartisan think tank on gay rights in public policy based the estimate on a review of census data.
Isn't it illegal to discriminate against gay and transgender workers already?
Not at the federal level. 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 gender identity. Maryland has a law prohibiting discrimination based on sexual orientation; Virginia has no such laws.
What do Americans think of this issue?
About seven in 10 Americans favor protecting gay workers from job discrimination, according to a May poll by the Public Religion Research Institute.
Public support has climbed through the years. A CNN-Time magazine poll in 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 face "a lot of" or "some" discrimination at the office, according to a Pew Research Center poll in 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.
How long has Congress been debating ENDA?
Supporters have been trying since 1994, when Rep. Gerry Studds, D-Mass., and Sen. Edward Kennedy, D-Mass., first tried to pass the bill. Kennedy got the bill to the full Senate in 2001, but it didn't pass. Rep. Barney Frank, D-Mass., got the measure passed by the Democratic-controlled House in 2007, but it faltered in the Senate.
The bill cleared the Senate Health, Education, Labor and Pensions Committee with bipartisan support in July. A House version has been introduced, but not considered by committees.
Most ENDA opposition comes from Republicans. What don't they like about it?
They generally believe that the law is unnecessary because federal statute already prohibits workplace discrimination and many larger companies already ban the practice. Republican critics also worry that ENDA's broad mandate would cause greater legal risk for employers who are perceived to be discriminating against gay 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.
Will Congress pass ENDA this time?
The Senate is expected to pass the latest version as soon as this week with the support of all members of the Democratic caucus and at least five Republicans.
But the office of House Speaker John Boehner, R-Ohio, said Monday that he believes the legislation would "increase frivolous litigation and cost American jobs, especially small-business jobs."
Peyton M. Craighill and Scott Clement contributed to this report.