Employee Stock Option Plan

[Guest stockoption]

Bank A grants its employees stock options, plan does not have change of control agreement. Bank B purchases Bank A in a pooling purchase. Bank B does have a change of control agreement in their employee stock option plan. Bank C purchases Bank B, once again pooling purchase, and Bank B's employees are informed that their options immediately vest. Bank B tells original Bank A employees that there is a question as to whether their options will vest. Is this possible or is this discriminatory??