* Worker's fiancee had complained of bias at plant

* He was fired soon after company learned of her complaint

* Ruling upholds federal government's position

The U.S. Supreme Court ruled on Monday that a federal law barring retaliation against a worker for complaints about on-the-job discrimination also protected the employee's relative from unlawful dismissal.

The high court unanimously ruled for Eric Thompson, who was fired from his job at a stainless steel manufacturing plant in Kentucky after his fiancee, who also worked there, filed a discrimination complaint.

The eight-page opinion written by Justice Antonin Scalia overturned a U.S. appeals court ruling that the law only protected against retaliation against workers who file the discrimination claims.

Thompson's then-fiancee, Miriam Regalado, who is now his wife, filed a complaint with a federal government agency, the Equal Employment Opportunity Commission, claiming her supervisors discriminated against her because of her sex.

The agency informed the company, North American Stainless, of her complaint on Feb. 13, 2003. Thompson was fired less than a month later. The company said he was fired because of his job performance, not because of his fiancee's bias complaint.

Thompson then went to the agency and said he had been fired because of his fiancee's complaint. But federal courts threw out his lawsuit complaining of retaliation.

The Obama administration supported Thompson. It said the U.S. appeals court's ruling was wrong and that federal law barred an employer from firing the relative or other close associate of an employee who complains of discrimination.

Scalia said Thompson fell under the law's protections.

Thompson is not an accidental victim of the retaliation -- collateral damage, so to speak, of the employer's unlawful act. To the contrary, injuring him was the employer's intended means of harming Regalado. Hurting him was the unlawful act by which the employer punished her, Scalia said.

North American Stainless is a unit of Spain's Acerinox (ACX.MC), the world's No. 1 stainless steel producer.

The Supreme Court case is Thompson v. North American Stainless, No. 09-291.

(Reporting by James Vicini, editing by Stacey Joyce)