"While employers are given a buffer for the A Penalty (an employer can fail to offer 5% and the penalty is not assessed for the first 30 employees), the penalty's nickname, the `sledgehammer' penalty, is well-earned, since the penalty applies to all of the employer's full-time employees in the EIN if triggered," said Laura Bibb, a compliance attorney for Lockton.

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"Generally, the coverage provides minimum value if the plan's share of the total allowed costs of benefits provided under the plan is less than 60% of those costs," she said. "Coverage is considered affordable for an employee if the employee's required contribution for self-only does not exceed a specified affordability percentage (set annually by the IRS) of the employee's household income.

"As a reminder, since employers generally do not know an employee's household income, the IRS allows employers to determine affordability using one of three affordability safe harbors (W-2, rate of pay and federal poverty level)."

The IRS is actively issuing 226-J letters to employers informing them that they may be liable for employer mandate penalties, Bibb said.

"Care should be taken to ensure full-time employees are properly identified and offered    coverage and that required employee contributions for self-only coverage are affordable under one of the three allowable safe harbors," she said. "Even still, errors on Form 1095-C can result in a Letter 226-J."