WASHINGTON — It was the first major piece of legislation that President Trump signed into law, and buried on Page 734 was one sentence that brought a potential benefit to the president’s extended family: renewal of a program offering permanent residence in the United States to affluent foreigners investing money in real estate projects here.

Just hours after the appropriations measure was signed on Friday, the company run until January by Mr. Trump’s son-in-law and top adviser, Jared Kushner, was urging wealthy Chinese in Beijing to consider investing $500,000 each in a pair of Jersey City luxury apartment towers the family-owned Kushner Companies plans to build. Mr. Kushner was even cited at a marketing presentation by his sister Nicole Meyer, who was on her way to China even before the bill was signed. The project “means a lot to me and my entire family,” she told the prospective investors.

The sequence of events offers one of the most explicit examples to date of the peril of the Trump and Kushner families maintaining close ties to their business interests and creates an impression they stand to profit off Mr. Trump’s presence in the White House. It also illustrates the problems of the so-called EB-5 visa program that prominent Republican and Democratic members of Congress want changed.

“It is just one more dilemma that a family with vast commercial interest has when relatives are in the federal government, particularly the White House,” said Michael H. Cardozo, who served as a deputy White House counsel in the Carter administration, which struggled with its own controversies related to the president’s brother, Billy Carter, and his work on behalf of an American company seeking to get into the oil industry in Libya. “The actions of relatives can come back and bite those serving those in the government.”