Which insurance plan requires all eligible employees to be covered?

The correct answer is that a non-contributory plan requires all eligible employees to be covered. In this type of plan, the employer pays the entire premium for the insurance, meaning that employees do not have to contribute financially to the premiums. As a result, since there are no employee contributions, employer coverage is mandatory, ensuring that all eligible employees are enrolled in the insurance plan.

In contrast, a contributory plan allows employees to share the cost of premiums with the employer, usually through payroll deductions. Because participation in contributory plans often depends on employees opting in and paying a portion of the premium, not all eligible employees may choose to enroll.

Regarding the single employer group plan, while it is applicable to a specific employer and its employees, it does not inherently require universal coverage for all eligible employees unless it's structured as a non-contributory plan. A multiple employer group plan covers employees from various employers, typically allowing for more flexibility in coverage options, but it also does not stipulate that all eligible employees must be covered.

Thus, the defining characteristic of a non-contributory plan is the requirement for mandatory coverage for all eligible employees without any contribution from them.