Am I considered covered by an employer sponsored retirement plan for the year if I do not participate in the plan or if I did not work long enough to be vested?
The answer to this question depends on your type of retirement plan. Generally, if your employer's plan has a separate account for each employee, it is a defined contribution plan. If any amount was contributed or allocated by you or your employer to your account, you are considered covered. It does not matter if you have worked long enough to be vested.
In the other type of plan, a defined benefit plan, the employer must make enough contributions (together with earnings) to provide the retirement benefit promised in the retirement plan. In this type of plan, if you meet the minimum age and years of service requirements to participate in your employer's plan, you are considered covered. It does not matter if you are vested.
The Form W-2 (PDF) you receive from your employer has a box used to indicate whether you were covered for the year. The "Pension Plan" box should have a mark in it if you were covered.