Some countries allow physicians to balance bill patients, that is, to bill a fee above the one that is negotiated with, and reimbursed by the health authorities. Balance billing is known for restricting access to physicians' services while supplemental insurance against balance billing amounts is supposed to alleviate the access problem. This paper analyzes in a theoretical setting the consequences of balance billing on the fees setting and on the inequality of access among the users of physicians' services. It also shows that supplemental insurance against the expenses associated with balance billing, rather than alleviating the access problem, increases it.