Generally, if an employee is offered affordable minimum essential coverage under an employer-sponsored plan, he is ineligible for a premium tax credit and cost-sharing reductions for health insurance purchased through a state or federal insurance Marketplace.

However, if the coverage is unaffordable (see below) or the plan’s share of benefits is less than 60%, then he is eligible, but only if he declines to enroll in the coverage and purchases coverage through the Marketplace instead.

IRS has clarified that the fact that an employer doesn't employ enough employees to be subject to the employer mandate does not affect its employees' eligibility for a premium tax credit. (Q&A 44)