Representative Duncan Hunter wore the United States Marine Corps’ iconic Eagle, Globe and Anchor emblem on his uniform for years when he deployed multiple times to Iraq and Afghanistan. But that evidently did not give him license to put it on his campaign materials more than a decade later.

Mr. Hunter, a Republican who has represented a conservative and heavily military district near San Diego since 2009, sent out a mailer this month attacking his opponent and some of his colleagues as radicals and terrorist sympathizers. On the envelope was the official United States Marine Corps emblem. This week, the California congressman got a letter from the Marine Corps telling him he did not have permission to use the symbol and should stop immediately.

The Marines said the Eagle, Globe and Anchor emblem was a registered trademark, along with the phrase “No better friend, no worse enemy,” which also appeared on the campaign materials.

“We thereby request your campaign immediately remove the emblem and the phrase from its mailers,” said the letter, which was first disclosed by NBC News.