The Environmental Protection Agency (EPA) is amending the electronic reporting requirements for the National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units (also known as the Mercury and Air Toxics Standards (MATS)) to allow for the temporary submission, through June 30, 2018, of certain reports using the portable document file (PDF) format and to correct inadvertent errors. With this action owners or operators of Electric Utility Steam Generating Units (EGUs) will be able to continue to use temporarily a single electronic reporting system for MATS data submissions, to rely on correct language for mercury (Hg) relative accuracy test audit (RATA) requirements, and to rely on the correct acceptance criterion for ongoing quality assurance test requirements for Hg RATAs. This extension will allow the EPA the necessary time to develop, implement, and test the code necessary so that all MATS reports required to be submitted electronically can be submitted using the Emissions Collection and Monitoring Plan System (ECMPS) Client Tool.