The Trump administration this year ordered federal border agents and customs officers not to attend events hosted by organizations that support women or minority groups in law enforcement, according to a senior border official.

Customs and Border Protection, the largest law enforcement agency in the federal government, issued a little-noticed internal memo in late March telling its officials not to attend events or conferences hosted by organizations like Women in Federal Law Enforcement and the National Organization of Black Law Enforcement Executives, or NOBLE, said the senior official, Timothy Quinn. Mr. Quinn worked at the agency for nearly 12 years until he retired on Friday as a result of the policy.

In an interview on Monday, Mr. Quinn said the directive was included in a broader travel advisory issued on March 28 to senior officials at the agency, who were then expected to pass along the instruction to the rank and file. The memo, which invoked President Trump’s executive order banning diversity practices across the federal government, barred attendance at events or conferences “that have a gender basis, race basis or a culture basis,” Mr. Quinn said.

“I think that’s discrimination,” said Mr. Quinn, the former head of Customs and Border Protection’s Office of Intergovernmental Public Liaison. “I don’t understand why we wouldn’t engage with these organizations to share this kind of information.”

In a statement, Tricia McLaughlin, a spokeswoman for the Department of Homeland Security, which oversees Customs and Border Protection, said the agency’s “personnel are free to participate in outside groups on their own time.”

“However, C.B.P. will not use taxpayer dollars and official duty hours to fund identity-based events or programs,” Ms. McLaughlin said. “As a federal law enforcement agency, our focus is on the mission.”