SEIU has no business being involved in the Health Care Reform discussion at all, since they have been exempted from the program (takeover). They have no legitimate interest, and are only present for intimidation purposes.
Most people don't know that. I think some protest signs that say something to the effect of 'Make the Unions pay, too!' might be effective.
It's not outright opposition to the plan, but it would be a deal breaker, and it puts both the politicians and the Union thugs on the defensive.