There is a safe harbor for your client, if he provided honest answers when he signed up for the market place insurance. From IRS.

A14. The regulations under Internal Revenue Code section 36B provide a safe harbor for certain affordability determinations made by the Marketplace. Under the safe harbor, employer-sponsored coverage is treated as unaffordable for an individual if when the individual enrolled in Marketplace coverage (1) the individual (or someone else on the individual’s behalf) provided accurate information to the Marketplace about the cost of employer-sponsored coverage for the individual (and other family members, if applicable) and (2) the Marketplace determined that advance payments of the Premium Tax Credit (APTC) could be made for the individual’s Marketplace coverage because the employer-sponsored coverage was unaffordable based on projected household income. Under these circumstances, a Premium Tax Credit would still be allowed for the individual’s Marketplace coverage if the other eligibility criteria are met, even though the employer-sponsored coverage would have been affordable based on actual household income. The safe harbor does not apply to you if, with reckless disregard for the facts, incorrect information was provided to the Marketplace concerning the portion of the annual premium for your coverage under the plan.