Free medical care at public expense came a few years ago in Jamaica with the passage of an Act of Parliament. In the mean time and since then, wage and/or salary negotiations often involve provisions for Group Medical Insurance. Now the small operations with healthy staff sometimes simply agree to pay the medical costs of their staff. That was the situation on my very first job.
Now when medical insurance becomes compulsory, some employers will opt to self-insure, especially those with healthy staff. Now, that causes a problem because if the ones who need it the least do not participate, then the per person premium will increase. That might be why a government might make it compulsory for all companies with 50 staff or more which is the usual minimum number of persons an insurer will accept.
To get around that and to save on premiums, some employers are opting for what is know as "Excess of Loss" cover. That is, the employer pays up to an agreed amount per person and the insurer picks up the balance. In such cases, up to 99% of the time, the insurer pays nothing, so the premium is tiny and the employer has met the requirements of the law; his employees are covered under a group medical insurance policy.
The other one that may be done is to buy what is known as "Stop Loss" cover. Under this type of cover, the employer chooses a limit of the total payment for medical care per period of insurance and if the total payments exceed that the insurance company reimburses the employer the difference up to an agreed amount. Again, the employer has met the compulsory insurance requirements under the law.
Why would companies do that? Simple, it can work out to be cheaper. Remember that the law allows that the employees also contribute to the premium, so if the self-insurance scheme plus either "Excess of Loss" and/or "Stop Loss" cover results in less premium, it would be stupid not to go that route. Remember that the employees are paying part of the premium, including the self- insurance cover.
Since such things amount to "selection against the insurer", I expect to see your medical insurance companies to lobby the U.S. government to either curtail or not allow such covers.
I'm watching to see how things turn out.