Looks like EB can announce a ban.

13.k.9 It shall be a violation of this Agreement if the Association
engages in any action to encourage or suggest to its members
that they not pick up open time or decline junior available
assignments. This language shall not be applicable during a
time of furlough or furlough announcement. Further, it shall be
a violation of this Agreement if any crewmember(s) takes any
action, individually or collectively, to discourage or interfere
with other crewmembers who desire to pick up open time or
accept junior available assignments. Nothing in the preceding
sentence shall limit an individual crewmember’s ability to voice
personal opinions.