If pre-Affordable Care Act (ACA) health insurance regulations returned with a repeal of the law, 52 million people under the age of 65—27 percent of the U.S. population—could be denied coverage on the individual market due to pre-existing conditions.

The Kaiser Family Foundation report said the majority of this non-Medicare-eligible population has insurance through their employer or Medicaid, but if they ever lost that coverage due to events like the loss of a job or a divorce, they could be essentially uninsurable without the ACA’s protections for pre-existing conditions.

“Before ACA protections took effect in 2014, private insurers in the individual health insurance market could use applicants’ health status, health history and other risk factors to determine whether and under what terms to issue coverage. Some examples of conditions which could have led to automatic denial of coverage include cancer, diabetes, epilepsy, heart disease, and pregnancy,” the foundation said.

Prior to the ACA, about 18 percent of applications for insurance on the individual market were denied, and more likely never bothered applying due to the likelihood they’d be rejected.

Should those pre-ACA underwriting practices return, the number of declinable people would vary greatly by state. Alabama has the highest percentage of pre-existing conditions among its non-elderly population, at 33 percent, while the greatest number of declinable adults would be in California, where more than 5.8 million people could be denied individual market coverage.

President-elect Donald Trump has said he wants to keep protections for pre-existing conditions while repealing the ACA. New York tried such a plan without the mandate to buy health insurance which the ACA included and the result was a “death spiral” in the individual insurance market.