Hugh:
The RLA hasn't changed in many years. It's called Agency Shop and it applies to all US unionized airlines. Membership is optional but if you're a non-member you pay either an Agency Fee equal to full union dues or you can be a dues objector and pay around 85% of full dues.
That assumes the "Union" was properly formed and working in the common interest of all parties. 2800 out of 5300 pilots are non payers. All 4 USAPA is attempting to fire are West...two are female. They'll lose arbitration and the company is loath to fire a pilot for non-payment. Why would they risk the discrimination suit?
USAPA and the merry band of impotents that run it are pathetic jokes.