I'm my province companies over a certain size (even those with a union) have to go through an evaluation process every 5 years to evaluate wages to prevent these situations. I know one person who got a 17% boost to her salary one year through this process and I also used to work a job where the employees in my department were mostly women and the employer and union were forced to sign a letter of agreement to increase everyone's wage in that department because it was lower than a similar job in another department with mostly men staff.