Grievance

[Sarah]

1 - a complaint about being treated in an unfair way:
have a grievance: People know who to go to if they have a grievance.
2 - a feeling that you have been treated in an unfair way:
sense of grievance: This sense of grievance began with the confiscation of their land.
nurse a grievance: For years he nursed a grievance against his former employer.

[Vania]

A real or imagined wrong or other cause for complaint or protest, especially unfair treatment.