<p>This article investigates the incentive and ability of a platform to limit the extent of competition between the sellers it hosts. Absent contractual restrictions, a platform has an incentive to ensure competition between the sellers. This incentive can change with the introduction of so-called platform most-favored nation clauses (PMFN) that require the online sellers not to offer better conditions on other distribution channels. Such clauses can align the interests between sellers and platforms to restrict competition. I illustrate that a platform can stabilize seller collusion to its own benefit. These results offer a novel rationale to treat PMFNs with scrutiny.</p>