A campaign finance watchdog group filed a complaint on Tuesday against a Canadian billionaire alleging that he violated a federal ban on contributions by foreigners when his United States-based company donated $1.75 million last year to a political committee supporting President Trump’s agenda.

The complaint was filed by the watchdog group, the Campaign Legal Center, with the Federal Election Commission against Barry Zekelman, the chief executive of Zekelman Industries, North America’s largest steel tube manufacturer. Mr. Zekelman has pushed the Trump administration to take steps that help block the import to the United States of steel tube made by his competitors.

Mr. Zekelman, whose efforts to influence federal policy on steel tariffs was detailed in a story in The New York Times, was invited to a dinner with Mr. Trump at the Trump International Hotel in April 2018, after the first contribution to the Trump-affiliated committee, America First Action Super PAC, for $1 million.

Two more contributions — first for an additional $250,000 and then $500,000 more — followed during 2018, making Zekelman Industries one of the single biggest contributors to Mr. Trump’s political causes.