Originally, the SEC did not adopt specific standards for determining which credit rating agencies were "nationally recognized", and instead addressed the question on a case-by-case basis. NRSRO recognition was granted by the SEC through a "No Action Letter" sent by the SEC staff. Under this approach, if a CRA (or investment bank or broker-dealer) were interested in using the ratings from a particular CRA for regulatory purposes, the SEC staff would research the market to determine whether ratings from that particular CRA are widely used and considered "reliable and credible." If the SEC staff determined that this was the case, it would send a letter to the CRA indicating that if a regulated entity were to rely on the CRA's ratings, the SEC staff would not recommend enforcement action against that entity. These "No Action Letters" were made public and could be relied upon by other regulated entities, not just the entity making the original request. The SEC later sought to further define the criteria it uses when making this assessment, and in March 2005 published a proposed regulation to this effect. According to the SEC: