In September, 2008, the FCC Enforcement Bureau has sent hundreds of letters to telecommunications carriers and providers of VoIP services subject to the FCC's CPNI rules. Although a 2007 CPNI compliance certificate was due to be filed with the Commission no later than March 1, 2008, many regulated companies had not filed their certificate as of early September. The FCC's Enforcement Bureau is investigating these potential violations of its CPNI rules by sending letters to all companies that file Form 499 Universal Service reporting forms requesting evidence of each company's 2007 CPNI compliance certificate filing. If no filing has been made, a detailed explanation must be provided. Responses are to be supported by an affidavit or declaration by an authorized and knowledgeable officer of the company. As an apparent result of this FCC Enforcement Bureau activity, a large number of 2007 CPNI certificate compliance filings were made in late September, 2008.