WASHINGTON (AFP) - A United States Supreme Court justice has blocked a stipulation in the new health care reform law that requires some religion-affiliated organisations to provide insurance that includes birth control.

Justice Sonia Sotomayor acted on Tuesday just hours before the Affordable Care Act law was to take effect, in response to an order of nuns in Colorado, US media reported.

She gave the government until Friday morning to file briefs on the matter.

The contraception requirement has been one of the most controversial aspects of the health law.

Religious opponents of abortion object to the requirement to provide emergency contraception pills.

As a compromise, the administration said that women who work for nonprofit religious groups that are against birth control could receive separate coverage not paid for by the employers.

But it refused to offer such assurances to secular businesses whose owners have religious objections to contraception.

That distinction has led to a separate group of lawsuits. Last month, the Supreme Court agreed to hear a pair of cases on whether corporations can deny insurance coverage for contraception.

Sotomayor's order applies to the Colorado nuns, the Little Sisters of the Poor, and other Roman Catholic nonprofit groups that use a health plan called the Christian Brothers Employee Benefit Trust.

The groups' lawsuit is one of many challenging the federal requirement for contraceptive coverage. But a decision on the merits of that case by the full Supreme Court could have broader implications, the New York Times said.