Which of the following actions would NOT initiate an investigation by TREC regarding a real estate license holder?

The action that does not initiate an investigation by TREC regarding a real estate license holder is the anonymous complaint submitted via telephone. Complaints need to provide sufficient detail and accountability to allow for proper investigation, which is not possible with anonymous submissions. When complaints are filed, TREC requires a clear identification of the complainant to follow up on the allegations and gather more information if necessary. Anonymous complaints lack the necessary details and verifiability that TREC needs to effectively pursue an investigation.

In contrast, a signed written complaint, evidence with a formal complaint, or a complaint alleging reasonable cause all provide sufficient grounds for initiating an investigation because they include identifiable information and direct allegations that TREC can act upon.