Ahead of a key vote, President Barack Obama has called on the US Congress to pass a law protecting workers against discrimination based on sexual orientation and gender identity.

The Senate is expected to take a vote today on whether to enshrine the Employment Non-Discrimination Act (ENDA) into law.

Writing in the Huffington Post, President Obama said: “Here in the United States, we’re united by a fundamental principle: we’re all created equal and every single American deserves to be treated equally in the eyes of the law. We believe that no matter who you are, if you work hard and play by the rules, you deserve the chance to follow your dreams and pursue your happiness. That’s America’s promise.”

But he warned: “And yet, right now, in 2013, in many states a person can be fired simply for being lesbian, gay, bisexual, or transgender.

As a result, millions of LGBT Americans go to work every day fearing that, without any warning, they could lose their jobs — not because of anything they’ve done, but simply because of who they are.

It’s offensive. It’s wrong. And it needs to stop, because in the United States of America, who you are and who you love should never be a fireable offense.”

He added: “That’s why Congress needs to pass the Employment Non-Discrimination Act, also known as ENDA, which would provide strong federal protections against discrimination, making it explicitly illegal to fire someone because of their sexual orientation or gender identity. This bill has strong bipartisan support and the support of a vast majority of Americans. It ought to be the law of the land.”

Last week, West Virginia Senator Joe Manchin became the 54th Democratic senator to back ENDA, meaning all 55 are now in favour of the reform.

President Obama called on Republicans to do the same. “Several Republican Senators have already voiced their support, as have a number of Republicans in the House. If more members of Congress step up, we can put an end to this form of discrimination once and for all.”

Invoking the spirit of Martin Luther King Jr, the President concluded: “In America of all places, people should be judged on the merits: on the contributions they make in their workplaces and communities, and on what Martin Luther King Jr. called “the content of their character.” That’s what ENDA helps us do. When Congress passes it, I will sign it into law, and our nation will be fairer and stronger for generations to come.

Writing in the Wall Street Journal on Monday, Apple Chief Executive Tim Cook also called on Congress to pass ENDA. “Those who have suffered discrimination have paid the greatest price for this lack of legal protection,” he said.