There are two types of contract modifications:
Except for certain mail transportation contracts, only contracting officers are authorized to sign contract modifications for the Postal Service. Other Postal Service personnel may not do as follows:
Contract modifications, including changes that can be issued unilaterally, must be priced before they are signed if it can be done without adversely affecting the interest of the Postal Service. If a significant cost increase could result from a contract modification and time does not permit negotiating a price, at least a maximum price must be negotiated whenever practicable.