Practically speaking, it "makes sense" to break the complicated law's implementation into stages, Beilenson said. Still, he added, having any uninsured people at all strains the resources of hospitals and taxpayers.

Republican lawmakers on Capitol Hill, who are still trying to derail implementation of the law, kept up their criticism.

"This announcement means even the Obama administration knows the 'train wreck' will only get worse," House Speaker John A. Boehner, an Ohio Republican, said in a statement. "I hope the administration recognizes the need to release American families from the mandates of this law as well."

The administration has given no indication that it plans to delay the penalty on Americans who do not get coverage, which is slated to start at $95 next year.

The so-called employer mandate is not as central to the law as other provisions of the huge legislation.

Coverage rates are already very high among large and medium-sized businesses. Among employers with more than 200 employees, 98 percent offer health benefits, according to an annual survey by the nonprofit Kaiser Family Foundation and the Health Research & Educational Trust. And 94 percent of employers with between 50 and 199 employee provide health insurance, the survey found.

Under the law, large employers that did not provide coverage would be fined $2,000 per employee beyond the first 30 employees.

Small businesses are less likely to offer health benefits, but these employers are exempt from the health law's mandate.

The mandate nonetheless has been a lightning rod for criticism in the business community, particularly for employers that rely on part-time workers.

The complex method used to assess penalties on employers required multiple computer systems to track the number of hours employees worked, whether they could afford coverage and whether they qualified for federal aid if they did not get health insurance at work.

Particularly nettlesome for many employers is the law's system of calculating full-time and part-time workers. The law exempts employers with fewer than 50 employees who work at least 30 hours a week.

That system prompted warnings from many businesses and even some supporters of the law that many employers would shift employees to part-time work to avoid the penalty.

The Treasury Department indicated Tuesday it would provide further details later this summer about how it will implement the penalty in 2015.

Baltimore Sun reporter Carrie Wells and Tribune Newspapers staff writer Chad Terhune in Los Angeles contributed to this article.