Employees have the right to quit their job for just cause, and claim damages for severance pay, in certain limited circumstances. If the employer unilaterally and without notice reduces the employee’s pay, substantially changes their job duties or job title, or increases the employee’s hours, then the employer has forced a fundamental change to the employment agreement on the employee and the employee would have just cause to quit. Temporary lay-offs and job relocation can be considered just cause to quit, as can harassment, bullying, or a toxic workforce.
The remedy for a constructive dismissal is to quit and seek severance pay, which would be assessed as if you had been dismissed without just cause.
Arguably, employers can give you reasonable notice of a substantial change in your employment contract, similar to giving reasonable notice of termination, in which case you would have no remedy.
Further, employees have a duty to mitigate their losses, i.e. reduce their damages, which may require employees to accept some kinds of just cause to quit, such as a change in job duties for the same pay, so long as continuing to work doesn’t result in hostility, embarrassment, or humiliation.
If you think you may have been constructively dismissed, you should seek legal advice immediately and before making critical decisions.