Grievances are for violations of the CBA, not because you wish to renegotiate the CBA.   RLA is about major and minor disbutes.   The RLA categorizes all labor disputes as either "major" disputes, which concern the making or modification of the collective bargaining agreement between the parties, or "minor" disputes, which involve the interpretation or application of collective bargaining agreements.  Section 6 notification is for major disputes in rebargaining the CBA, and grievances are about minor disputes violating or interpreting the existing CBA.   There isn't a violation in the CBA occuring, so a "class action" grievance is inappropriate.