Apple CEO Tim Cook is urging passage of a federal law that would protect workers from facing discrimination based on their sexual orientation.

In an op-ed column in Monday's Wall Street Journal, Cook writes that protections for lesbian, gay, bisexual and transgender workers is a good business practice that should be recognized in federal law.

"For too long, too many people have had to hide that part of their identity in the workplace," he wrote. "Those who have suffered discrimination have paid the greatest price for this lack of legal protection. But ultimately we all pay a price. If our co-workers cannot be themselves in the workplace, they certainly cannot be their best selves."

At issue is the Employment Non-Discrimination Act, known as ENDA, which faces a key vote in the Senate on Monday.

The bill cleared a Senate procedural vote late Tuesday. Supporters are hoping the bill passes the Senate, which it could do with the support of all 55 Democratic senators and at least a handful of Republicans. Legislation needs 60 votes in the Senate to avoid being subject to a filibuster.

While the majority of U.S. workers live in states that bar employment discrimination based on sexual orientation, 29 states still allow employers to fire workers based on their sexual orientation. An additional four states allow the firing of transgender workers even if gay employees have protection.

The federal law would protect both gay and transgender employees.

While chances for passage in the Democratic-controlled Senate look good, the outlook is less clear in the Republican-controlled House. Many conservative groups, including the Heritage Foundation and the Family Research Council, are actively fighting the legislation.

Cook, who became CEO of Apple in 2011, has typically not taken positions on public issues outside of those directly affecting Apple's operations, such as taxation of multinational corporations.

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A number of major employers, including Exxon Mobil (XOM) and Wal-Mart (WMT), have started to offer employee benefits such as health coverage to same-sex couples.

More than 90% of the Fortune 500 companies have adopted written nondiscrimination policies explicitly prohibiting harassment and discrimination on the basis of sexual orientation, according to the Human Rights Campaign, a group that is pushing for the legislation.

But public support for ENDA has been more limited. The U.S. Chamber of Commerce has been neutral on the legislation.

Exxon Mobil shareholders recently rejected a shareholder proposal that would have offered explicit protections to LGBT workers. Exxon Mobil management had argued the measure was unnecessary due to its existing prohibition against discrimination.