Have you read their constitution? It's spelt out very clearly. I've cut and pasted it below for you, and all others interested, to understand:
6. All members of the Club will abide by the following Rules of the Trail, endorsed by MTBA and the International Mountain Bicycling Association:
a. Ride On Open Trails Only.
Respect trail and road closures (ask if uncertain); avoid trespassing on private land; obtain permits or other authorization as may be required. Federal and state Wilderness areas are closed to cycling.
Any Member found in breach of one or more rules of the trail may be subject to expulsion from the Club in accordance with Section 33.
33. (1) Subject to this rule, the committee may expel a member from the Club if, in the opinion of the committee the member has been guilty of conduct detrimental to the interests of the Club.
http://www.wmbc.asn.au/Forms/CONSTITUTION2.pdf