Can a union establish a prototype 401(k) plan? It is not clear to me how the union can be the "employer." Or is this treated as such under Code Section 413(b)? Would it have to be jointly administered as a Taft-Hartley plan? Thanks.

Perhaps check IRS Rev. Proc. 2005-16, which seems to indicate they cannot. If anyone has been successful with a protoype, I would like to know, as it would be much less expensive.

Ok, as long as the plan covers only employees of the adopting employer. See Rev Proc 2005-16:

Areas Not Covered by Opinion Letters - Opinion letters will not be issued for:

(1) Multiemployer plans and multiple employer plans;

(2) Union plans (This does not preclude an M&P plan from covering employees of the employer who are included in a unit covered by a collective bargaining agreement or the adoption of an M&P plan pursuant to such agreement as a single employer plan that covers only employees of the employer.);