It's unfortunate that such a small issue, monetarily speaking, has been allowed so much attention from your board. At $5 a pop, the total is a tiny fraction of your $25k budget. The bigger question is WHY the teachers don't join the PTO and fix the underlying reasons versus trying to figure out how to force a membership.
When arguing the motion, I suggest you position your opposition from a public relations perspective: How Will Forcing a PTO Membership on our Teachers Affect Our Organization?
Prior to the meeting where this motion will be voted upon, interview several of the most well respected teachers to determine how they would perceive the automatic membership deduction from their class money. Ask why they haven't voluntarily joined the PTO in the past. Write down their quotes exactly. Do the same with the principal. Present these comments during the debate and express your concern regarding the potential damage to the good working relationship between the teachers and the PTO that will ensue if the "auto-deduct" motion will pass, particularly since the class money is such a small amount anyway.
Also, prior to the meeting, call a few of the more influential/respected/experienced board members to guage their perspective. Share your concerns as well. Then, you'll better know what you're up against when you walk in the next meeting.
Also, it's not enough to just fight a motion if a bonified problem exists. Along with your opposition to this motion, suggest alternatives to solve the teacher membership problem or suggest that, ultimately, it's not really a problem that needs attention at all.
If the VP leaves in a huff over a calm presentation of an opposing view, you don't want her on the board anyway, so quickly vote to accept her resignation so she can't reconsider and withdraw it. If she stays and is a pill, your by-laws should have a clause regarding board members behavior towards one another. If the by-laws have no such clause, draft one and get it passed, then you can deal with her from that perspective.
I am the new PTO president and it didn't take long to get into a disagreement with one of my board members. At our first meeting, we were discussing our membership income and how many of our teachers join the PTO. We are a small school in an upper middle class district with around 250 families. Our annual budget is about $25,000 which is the smallest budget in the district. In past years we have offered the teachers a membership in the PTO the same as the parents. Unfortunately, only 3 or 4 of the 66 staff members actually paid the $5 to join the PTO. Everyone on the board agrees that this level of teacher participation in the organization is just terrible. We give all the full time and part time teachers start up cash, $50 and 25 respectively. After some quick discussion, we decided to reduce the amount of start up cash by $5 and automatically give them membership. I thought about this a few days later and thought it was a very bad decision. I contacted the VP of Membership and presented an alternative. We could offer our teacher's an honorary membership free of charge. Unfortunately, the VP of Membership adamantly disagrees with me and is arguing her position to the rest of the Board. She has a very strong personality and I honestly don't see how to come out of this in a good way. If, as I suspect, the rest of the board disagrees with her, then I fear she will walk off in a huff and not be on the board or worse stay on the board and be a thorn in my side the whole year. If however, the board agrees with her, then I think we are making a very bad decision and risk alienating the teachers.
How do I exercise authority as the head of the board without appearing like a dictator?