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.