A far-reaching bill aimed at barring products made with forced labor in China became law after President Biden signed the bill on Thursday.

But the next four months — during which the Biden administration will convene hearings to investigate how pervasive forced labor is and what to do about it — will be crucial in determining how far the legislation goes in altering the behavior of companies that source products from China.

While it is against U.S. law to knowingly import goods made with slave labor, the Uyghur Forced Labor Prevention Act shifts the burden of proof to companies from customs officials. Firms will have to proactively prove that their factories, and those of all their suppliers, do not use slavery or coercion.

The law, which passed the House and Senate nearly unanimously, is Washington’s first comprehensive effort to police supply chains that the United States says exploit persecuted minorities, and its impact could be sweeping. A wide range of products and raw materials — such as petroleum, cotton, minerals and sugar — flow from the Xinjiang region of China, where accusations of forced labor proliferate. Those materials are often used in Chinese factories that manufacture products for global companies.

“I anticipate that there will be many companies — even entire industries — that will be taken by surprise when they realize that their supply chains can also be traced back to the Uyghur region,” said Laura Murphy, a professor of human rights and contemporary slavery at Sheffield Hallam University in Britain.

If the law is enforced as written, it could force many companies to rework how they do business or risk having products blocked at the U.S. border. Those high stakes are expected to set off a crush of lobbying by companies trying to ease the burden on their industries as the government writes the guidelines that importers must follow.

“Genuine, effective enforcement will most likely mean there will be pushback by corporations and an attempt to create loopholes,” said Cathy Feingold, the international director of the A.F.L.-C.I.O. “So the implementation will be key.”

Behind-the-scenes negotiations before the bill’s passage provided an early indication of how consequential the legislation could be for some of America’s biggest companies, as business groups like the U.S. Chamber of Commerce and brand names like Nike and Coca-Cola worked to limit the bill’s scope.

The Biden administration has labeled the Chinese government’s actions in Xinjiang — including the detention of more than a million Uyghurs and other predominantly Muslim minorities, as well as forced conversions, sterilization and arbitrary or unlawful killings — as genocide.