What is a material adverse change clause in a contract and can it be invoked in Ontario?

A material adverse change (MAC) clause — sometimes called a material adverse effect (MAE) clause — appears in many commercial contracts, particularly share purchase agreements and merger transactions. It typically allows a buyer to walk away from a deal (or renegotiate) if a defined "material adverse change" has affected the target business between signing and closing.

What constitutes a MAC is almost entirely determined by how the clause is drafted. Courts in Ontario (and Canadian courts generally) look carefully at the specific definition in the agreement: which events are included, which are excluded (macro-economic downturns, industry-wide trends, and pandemic effects are often excluded), and whether the effect on the business must be long-lasting rather than temporary.

Proving that a MAC has occurred is a high bar. Courts have been reluctant to allow buyers to escape deals simply because conditions changed; the change generally must be durationally significant and substantial in impact.

If you are in a transaction where you believe a MAC has occurred — or the other side is claiming one — the specific wording of the clause is everything. These are high-stakes disputes that require specialized commercial litigation advice, and the analysis is intensely document-driven.