What action can a System Administrator take to temporarily prevent a User from logging into Salesforce?

To temporarily prevent a user from logging into Salesforce, the most effective action a System Administrator can take is to freeze the user's account. Freezing an account stops the user from accessing the Salesforce platform without deleting their account or affecting their data in any way. This action is particularly useful when an administrator needs to restrict login access while retaining the user's information for potential future use.

Freezing an account maintains the user's settings and data intact, allowing for convenient reactivation later when access is needed again. Other options, such as deleting the user's account or resetting their password, are more permanent actions that do not allow for easy restoration of access. Changing the user's login hours could potentially restrict access but does not provide an immediate and complete block against logging in at all times.