What Must a Workplace Investigation Actually Include in 2025?

Workplace investigations are no longer just a best practice—they are a strict legal requirement under Ontario law. When an employer receives a complaint or becomes aware of an incident of workplace harassment, discrimination, or serious misconduct, failing to investigate properly can lead to significant liability, including human rights damages, constructive dismissal claims, and occupational health and safety penalties.

However, simply conducting an investigation is not enough. The investigation must be procedurally fair, unbiased, and thorough. Recent case law, including the 2025 Ontario Court of Appeal decision in Metrolinx v. ATU Local 1587, has further clarified the strict standards employers must meet.

“A flawed investigation is often worse than no investigation at all.”

1. Which law applies

In Ontario, the requirement to investigate stems primarily from two statutes:

• The Occupational Health and Safety Act (OHSA): Requires employers to investigate incidents and complaints of workplace harassment (including sexual harassment) "appropriate in the circumstances."
• The Human Rights Code: Requires employers to investigate allegations of discrimination or harassment based on protected grounds (e.g., race, sex, disability). Failure to investigate is considered a separate breach of the Code.

2. When are you legally required to investigate

An employer's duty to investigate is triggered not only by a formal written complaint but also when the employer becomes aware of an incident through informal channels, rumors, or direct observation. You cannot ignore a toxic work environment simply because no one has filed a formal grievance.

3. Who should conduct the investigation

The investigator must be objective and impartial. Depending on the severity and complexity of the allegations, this could be:

• An internal HR professional (if they have no prior involvement or conflict of interest).
• An external, independent investigator (often a lawyer or specialized consultant).

External investigators are highly recommended for allegations involving senior management, systemic issues, or where litigation is highly probable.

4. The seven elements every investigation must include

To meet the legal standard of procedural fairness, an investigation must generally include:

1. Promptness: The investigation must begin quickly (usually within days of the complaint) and conclude within a reasonable timeframe (typically 90 days, unless there are extenuating circumstances).
2. Notice: The respondent must be informed of the specific allegations against them in sufficient detail to allow them to respond.
3. Opportunity to Respond: The respondent must be given a fair chance to tell their side of the story and provide evidence.
4. Witness Interviews: The investigator must interview relevant witnesses identified by both the complainant and the respondent.
5. Evidence Collection: Relevant documents, emails, messages, and video footage must be gathered and reviewed.
6. Confidentiality: Information should only be shared on a strict "need-to-know" basis to protect the integrity of the process and the privacy of those involved.
7. A Written Report: The investigator must produce a report detailing the steps taken, the evidence gathered, and a clear conclusion on whether the allegations are substantiated on a balance of probabilities.

5. After the investigation: disclosure and corrective action

Under the OHSA, employers must inform both the complainant and the respondent, in writing, of the results of the investigation and any corrective action that has been or will be taken. If the allegations are substantiated, the employer must take appropriate disciplinary or remedial action to ensure a safe workplace.

6. Five common investigation mistakes

• Delaying the start: Waiting weeks to begin interviewing witnesses degrades evidence and signals a lack of seriousness.
• Failing to provide particulars: Ambushing the respondent with vague allegations denies them procedural fairness.
• Confirmation bias: An investigator who decides the outcome before gathering all the facts taints the entire process.
• Promising absolute confidentiality: You cannot promise a complainant that their identity will be kept secret from the respondent if the respondent needs that information to defend themselves.
• Ignoring the report: Commissioning an investigation and then failing to implement its recommendations exposes the employer to significant liability.

Conclusion

A flawed investigation is often worse than no investigation at all. It can compound the harm to the employees involved and drastically increase the employer's legal exposure. By ensuring your investigations are prompt, impartial, and procedurally fair, you protect both your workforce and your organization.