A memorandum of understanding (MOU) is a legal document but it is not necessarily legally binding; although in the realm of Union contract negotiations typically indicates a legally binding provision on a specific issue to be included in the contract OR indicates a temporary agreement (e.g. on COLAs for the year) that will be honored during the period of contract negotiations. The specific intent and language of the agreement will determine whether it is actually binding or not.
Below are links to the agreed and signed Memoranda of Understanding between the CPPW and the City of Portland.