Without ASPEP, management can make up and apply personnel policies anyway it wants.
When you are protected by the ASPEP/Company contract, your rights are spelled out in writing, and management is legally required to respect them.
If you face an unfair performance review, discrimination, harassment, dismissal, or denial of rights or benefits under the contract, ASPEP is at your side.
ASPEP representatives are available to help when disputes with management arise. They argue members' cases in accordance with the contractually specified grievance procedure -- a workplace judicial system with progressive steps. If the member and the association remain unsatisfied with the results, they can take the case before a neutral arbitrator (judge), who is selected by both sides -- management and ASPEP. Both are legally bound to obey the arbitrator's decision.
Because of ASPEP, management no longer has the final say.