WASHINGTON — In a first-of-its-kind ruling, the agency that enforces the nation’s job discrimination laws has ruled that transgender people are protected from bias in the workplace.

The decision late last week from the Equal Employment Opportunity Commission said that a refusal to hire or otherwise discriminate on the basis of gender identity is by definition sex discrimination under federal law.

While some federal courts have reached the same conclusion in recent years, employment law experts say the EEOC decision is groundbreaking because it sets a national standard of enforcement that offers employers clear guidance on the issue.

“This decision is important because the EEOC is the agency with lead authority to interpret and enforce the nation’s employment rights laws,” said Jennifer Pizer, legal director of the UCLA School of Law’s Williams Institute on Sexual Orientation and Gender Identity Law and Public Policy.

The case involved a California woman who claimed she was denied a contractor job with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives after the contractor learned she had undergone a procedure to change her gender from a man to a woman.

Mia Macy, an Army veteran and former police detective, initially applied for the position as a man and was told that she was qualified for the job as a ballistics technician. Then she informed the contractor that she was changing her gender. After that, she was told funding for the job was cut. She later learned someone else was hired for the position.

Macy filed a complaint with the ATF, which told her that federal job discrimination laws did not apply to transgender people. The Transgender Law Center, a legal rights advocacy group in San Francisco, took up her case.

The ruling does not yet determine that she was discriminated against, but that she can bring a charge of discrimination under the law.

EEOC spokeswoman Justine Lisser said the unanimous ruling from the five-member agency does not create a new cause of action. It clarifies that charges of gender stereotyping are considered claims of sex discrimination under existing law.

Until now, Pizer said, it was common for transgender workers to have their complaints rejected by EEOC regional offices and state civil rights agencies due to confusion about the state of the law.

“This is a confirmation that the courts are correct, so public and private employers coast to coast now have the benefit of the EEOC making this clear,” she said.

Currently 16 states and the District of Columbia have laws prohibiting discrimination based on gender identity. Mark Snyder, a spokesman for the Transgender Law Center said that EEOC offices in the remaining states would now have to heed the new decision.

Federal employment discrimination laws cover private and public employers with 15 or more employees.