Hillary Clinton's chief campaign strategist met with Colombia's ambassador to the U.S. on Monday to discuss a bilateral free-trade agreement, a pact the presidential candidate opposes.

Attendance by the adviser, Mark Penn, was confirmed by two Colombian officials. He wasn't there in his campaign role, but in his separate job as chief executive of Burson-Marsteller Worldwide, an international communications and lobbying firm. The firm has a contract with the South American nation to promote congressional approval of the trade deal, among other things, according to filings with the Justice Department. (See the related article.)

Penn, Schoen & Berland Associates, Mr. Penn's campaign-consulting firm, received more than $10 million in payments from the Clinton campaign as of the end of February, according to federal election filings.

Mr. Penn declined to comment. Howard Wolfson, communications director for Sen. Clinton's campaign, said in an email that "Mark was not there on behalf of the campaign" and referred further questions to Burson-Marsteller. "Sen. Clinton's opposition to the trade deal with Colombia is clear," Mr. Wolfson added.

A Burson-Marsteller spokesman didn't return calls or emails seeking comment.