WASHINGTON — The Trump administration has substantially scaled back paid leave requirements for employers that were created by a new coronavirus relief law, effectively exempting many small businesses in a move that infuriated lawmakers who had fought to expand the benefit.

In guidance issued on Wednesday, the Labor Department said that employers at companies with fewer than 50 workers had broad latitude to decline to offer the 12 weeks of paid leave that the law required for workers whose children were home from school or for child care because of the coronavirus pandemic. The legislation, which provides two weeks of paid sick leave and 12 weeks of paid family leave, and reimburses employers for it with tax credits, already excludes workers at companies with more than 500 employees.

In all, more than 75 percent of American workers are at companies that qualify for exemptions from the law.

Enacted in March, the law said that businesses with fewer than 50 employees could be exempted from providing the leave if it would prevent the business from functioning, leaving it to the Department of Labor to specify what that meant. The department on Wednesday issued its guidelines, giving an expansive definition that allowed small businesses significant leeway not to provide the leave. Under the guidelines, small businesses cannot be exempted from providing sick leave for an employee’s own illness.