In the latest report to undercut President Obama's "If you like your health care plan, you can keep it" promise, the Congressional Budget Office projects millions of workers will leave employer-sponsored health plans over the next decade because of ObamaCare.

Some will opt to go on Medicaid, but others will be kicked off their company plans by employers who decide not to offer coverage anymore, according to a new CBO report titled, "Federal Subsidies for Health Insurance Coverage for People Under Age 65: 2016 to 2026."

"As a result of the ACA, between 4 million and 9 million fewer people are projected to have employment-based coverage each year from 2017 through 2026 than would have had such coverage if the ACA had never been enacted,” the report, released Thursday, said.

Employers now cover some 155 million people, about 57 percent of those under 65. That's expected to decline to 152 million people in 2019. Ten years from now, employers will be covering about 54 percent of those under 65.

CBO said part of the shrinkage is attributable to the health care law: some workers may qualify for Medicaid, which is virtually free to them, and certain employers may decide not to offer coverage because a government-subsidized alternative is available.

Larger employers would face fines if they take that route.

But the agency also noted that employer coverage had been declining due to rising medical costs well before the health care law was passed, and that the trend continues.

The CBO also found that more people will enroll in Medicaid than previously predicted, though fewer will be covered through the public insurance marketplaces mandated by the Affordable Care Act.

The analysis underscores the view that the health care law is driving the nation's gains in insurance coverage, which raises political risks for Republicans who would repeal it.

The Associated Press contributed to this report.