The law is such an inconvenient thing: The EPA is attempting to enforce a regulation requiring ships to use low-sulfur fuel, despite the fact that the regulation has not yet been voted on by the Senate.
The treaty amendment at issue is a 2010 agreement under the International Convention for the Prevention of Pollution from Ships, or MARPOL. The United States has signed onto MARPOL, and Secretary of State Hillary Clinton has accepted the 2010 amendment. Domestic enforcement of the amendment is not permitted without ratification by two-thirds of the U.S. Senate.
And the Senate has not voted on this yet.