Can Your Employer Discipline You for Social Media Posts? What Unionized Workers Need to Know

You post something after work. A shot at the boss. A complaint about the conditions. An opinion about the news. A few days later they call you in about it. Can they discipline you for something you wrote on your own time?

Sometimes. Not every post is just cause. The words, the connection to the workplace, the policy they say you broke, and what actually happened at work all matter. For unionized workers, the grievance is how you test that. Do not assume the screenshot ends the argument.

Off duty is not invisible

What you do on your own time is not automatically the company’s business. It becomes their business when the post has a real connection to the workplace. Arbitrators look at whether you can be tied to the employer, how public it was, what you said, and whether it landed on the shop: a co-worker targeted, confidential information out, a working relationship wrecked, a rule you were told about and ignored.

• Threats or harassment aimed at a co-worker.
• Discriminatory or hateful comments that follow people into work.
• Confidential information from the workplace.
• Naming the employer while you torch it in public, when the book or a real policy speaks to that.
• A clearly communicated rule you actually broke.

Embarrassing a manager, or having an unpopular opinion, is not automatically discharge. A private argument among a few people is not the same as a public post that names a co-worker. Privacy settings are not a guarantee. Screenshots travel.

The Metrolinx case

In Ontario, Metrolinx fired five members of ATU Local 1587 over sexist messages in a private WhatsApp group on their own phones. The first arbitrator put them back. The Court of Appeal did not leave it there. In Metrolinx v. Amalgamated Transit Union, Local 1587, 2025 ONCA 415, the court said an employer can have a duty under the Occupational Health and Safety Act to investigate workplace harassment even when nobody filed a complaint, and that off-duty messages are not automatically out of reach if they affect the workplace.

The case went back. A new arbitrator decided it in ATU, Local 1587 v. Metrolinx, 2025 CanLII 114848. The conduct was serious enough for real discipline. Discharge was too much. The penalty that stuck was suspensions, not the street. That is the Wm. Scott question in real life: cause for some discipline, then was this penalty too much. Private is not a wall. It is also not an automatic firing.

Criticizing the boss is not the same as harassment

Unsafe work, unfair treatment, staffing, the schedule. Raising those is not automatically misconduct. How you raise them can be. Personal attacks, threats, discriminatory remarks, and leaking confidential information are separate problems. Speaking as a union member about a workplace issue is not the same thing as a public pile-on that names co-workers.

If the problem is real, use the channels that exist. Tell the steward. Keep your notes. Do not post the confidential part, and do not name people you do not need to name.

If they call you in about a post

• Ask which post, and which rule they say you broke. Do not guess.
• Keep a copy. Deleting it does not delete their screenshot.
• Open the collective agreement: discipline, investigations, representation, and the time limit.
• If the meeting can lead to discipline, ask for your steward before you answer the substance. An investigation is not a chat.
• Do not pour gas on it online while they are still looking.

They have to justify the penalty. You do not have to fill their silence. If they send you home without pay while they decide, that is its own question.

So: can your employer discipline you for a social media post? Sometimes, when the post is tied to the workplace and they can prove just cause for the penalty they picked. Not because you had an opinion on your own time. Think before you post. Do not leak confidential information. If they call you in, call the union before you start explaining.