Even without the mandate, 250.9 million people will have coverage, compared to 251.1 million — only 200,000 more — if the mandate remains intact, researchers said.

The mandate requires that businesses with 50 or more employees offer health insurance — or face a penalty if one of their employees qualifies for subsidized coverage in the marketplaces and the business does not offer health insurance.

The administration has so far twice delayed the mandate, a key piece of Obamacare.

Under the latest delay, employers with between 50 and 99 employees have until January 2016 to offer health insurance or pay a fine, and employers with more than 100 employees must offer insurance or pay a fine of $2,000 per worker by January 2015. Companies with fewer than 50 employees are exempt.

Researchers at the Urban Institute, who prepared the research for the Robert Wood Johnson Foundation, said that though 500,000 fewer people will get health insurance through their employer if the mandate is eliminated, the majority of them would find coverage through the law's exchanges.

"Many will benefit from subsidies to help purchase coverage," researchers said. "Still others will be eligible for Medicaid."

They also pointed to one positive impact that killing the mandate would have: lessening opposition to the law within the business community. Researchers said it would likely "lessen the chance of potential hiring practices that would have negative effects on some employees, such as employers hiring fewer people, hours cut to part-time employment."

"The employer mandate, along with its potential merits and drawbacks, has long been debated," said Andy Hyman, who works on coverage issues at the Foundation. "The research shows that eliminating it certainly wouldn't spell disaster and could calm worries of employers and help them see the virtues of reform."

The White House last month insisted that PPACA's employer mandate will — and must — remain part of the law.