Standing our ground on issues we feel convicted about is important to stay healthy but it does leave us open to the potential 'fallout'. It sure doesn't seem like you would be fired over this, though, unless it is in your job description and your refusal violated that.

If during your appraisal you discover that your position on unpaid meetings is causing problems, maybe there is a way you can negotiate this issue with your boss in a way that works for everyone.