EPA and the U.S. Coast Guard announced on June 27, 2011, that they have entered into a memorandum of understanding (MOU) in which they agree to jointly enforce U.S. and international air pollution requirements for vessels operating in U.S. waters. The requirements established limits on nitrogen oxides emissions and mandate the use of fuel with lower sulfur content.

Specifically, the MOU is an agreement to jointly enforce Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL), which is the primary international treaty addressing air pollution prevention requirements for ships. It was implemented in the United States through the Act to Prevent Pollution from Ships, 33 U.S.C. §§ 1901-1915. Under the MOU, each agency will conduct inspections and investigations and bring enforcement actions, if warranted. The agencies will develop new protocols for carrying out enforcement on vessels and in ports and other facilities, and will share information. The two agencies also notified the regulated community about the MOU and its contents by letter.