WASHINGTON — Workers who complain to their employers about wage violations are protected from retaliation whether the complaints are oral or written, the Supreme Court ruled on Tuesday in a 6-to-2 decision.

The question in the case, Justice Stephen G. Breyer wrote for the majority, was whether the phrase “filed any complaint” in the Fair Labor Standards Act of 1938 applied only to written complaints.

The case arose from complaints Kevin Kasten said he made to his former employer about where it kept the time clocks that recorded the hours he worked at a Wisconsin manufacturing plant. Though workers had to wear protective gear that took time to put on and take off, the time clocks were in an area beyond the changing area.

That was, a federal judge later found in a related case, a violation of the 1938 law.

Mr. Kasten said he had complained about the practice orally to a shift supervisor and to his employer, the Saint-Gobain Performance Plastics Corporation, through its grievance procedure.