Generally speaking, employees who are members of a union are not employed at will. At-will employees may be let go by their employer at any time, for any reason or no reason, with or without cause and with or without notice, just as the employee has the right to end the working relationship at any time, for any reason or no reason, with or without notice.
When workers are members of a labor union, their employment is going to be governed by a collective bargaining agreement which limits the employer’s right to discharge employees, by (1) requiring the employer to show “cause” for discharging an employee and (2) by proscribing a set procedure the employer needs to go through before a union employee can be terminated. Because the employer is going to have to be able to prove that it had sufficient “cause” to let the employee go, that employee is not employed at-will.
The bargaining agreement will define what is considered sufficient “cause” for discharge. Most likely it will include such situations as violation of workplace policies, insubordination, repeated and intentional gross misconduct, or job performance at very unsatisfactory levels. Mild policy violations, occasional lateness, and other issues while troublesome to an employer may not be sufficient to let a unionized employee go. Collective bargaining agreements also may set the procedures for an employee who chooses to dispute his or her discharge, such as filing a grievance, where at-will employees have no such recourse unless they believe their employment was terminated for an unlawful reason such as discrimination or retaliation.