WASHINGTON — Federal prosecutors in Manhattan issued subpoenas in recent weeks to several players in President Trump’s fund-raising apparatus as part of an investigation into two associates of Rudolph W. Giuliani who have been charged with violating campaign finance laws, according to people familiar with the investigation.

The subpoenas went to a lobbying firm run by a top fund-raiser for Mr. Trump, Brian Ballard, and to two people who have helped raise money for America First Action, a super PAC created to support the president and allied candidates, the people said.

Mr. Ballard and the America First fund-raisers worked to varying extents with Mr. Giuliani’s associates Lev Parnas and Igor Fruman, American citizens who helped Mr. Giuliani wage a pressure campaign on Ukraine that is now at the center of the impeachment inquiry into Mr. Trump.

The recent activity by prosecutors and F.B.I. agents shows that they have cast a wide net as they collect evidence about Mr. Parnas and Mr. Fruman, who were arrested last month. It also comes as the same prosecutors look into whether Mr. Giuliani, Mr. Trump’s personal lawyer, violated a federal lobbying law in some of his dealings with Ukrainians.