Can a public sector health plan, such as a retiree medical trust sponsored by a police officer association, be an ERISA plan? Our plan was advised that we do not have to be concerned about GASB reporting requirements because we are an ERISA plan. Does this make sense?

Doesn't make sense to me. While governmental plans are exempt from ERISA and (most) IRC rules, they are subject to GASB. If their position is that the plan is a collectively-bargained plan rather than a governmental plan, they could make an argument that it is not subject to GASB, but it would then be subject to FASB rules instead. (From the frying pan to the fire.) However, there are many rulings that a plan that covers governmental employees (whether under a CBA or not) is a governmental plan.

vebaguru:
You are correct about their being subject to GASB, but that is not mandatory.
States don't have to compy with GASB standards.
Texas is one unfortunate example.
Don Levit

Is it that Texas does not use GASB rules or is it that Texas opted out of GASB 45 only?

In any case there is no connection that I know of between ERISA reporting and GASB reporting. Two separate issues, two separate purposes.

To respond to your first question - whether such arrangement can be an ERISA plan, there are many DOL Advisory opinions on this subject. The issue is who the sponsor is and who funds the arrangement. Where the plan is sponsored by and funded by the employees through some voluntary group, there are several situations where the DoL has concluded that it is not a governmental plan and is subject to ERISA. See for example, DoL Advisory opinions 89-16, 79-39 or 92-19.