<P> Government contracts are governed by Federal common law, a body of law which is separate and distinct from the bodies of law applying to most businesses--the Uniform Commercial Code (UCC) and the general law of contracts . The UCC applies to contracts for the purchase and sale of goods, and to contracts granting a security interest in property other than land . The UCC is a body of law passed by the U.S. state legislatures and is generally uniform among the states . The general law of contracts, which applies when the UCC does not, is mostly common law, and is also similar across the states, whose courts look to each other's decisions when there is no in - state precedent . </P> <P> Contracts directly between the Government and its contractors ("prime contracts") are governed by the Federal common law . Contracts between the prime contractor and its subcontractors are governed by the contract law of the respective states . Differences between those legal frameworks can put pressure on a prime contractor . </P> <P> The authority to purchase is not one of the explicitly enumerated powers given to the Federal Government by Section 8 of Article One of the United States Constitution, but courts found that power implicit in the Constitutional power to make laws that are necessary and proper for executing its specifically granted powers, such as the powers to establish post offices, post roads, banks, an army, a navy, or militias . </P> <P> Behind any Federal Government acquisition is legislation that permits it and provided money for it . These are normally covered in authorization and appropriation legislation . Generally, this legislation does not affect the acquisition process itself, although the appropriation process has been used to amend procurement laws, notably with the Federal Acquisition Reform Act (FARA) and the Federal Acquisitions Streamlining Act (FASA). Other relevant laws include the Federal Property and Administrative Services Act of 1949, the Armed Services Procurement Act (ASPA) and the Anti-Deficiency Act . </P>

Who decides which laws are necessary and proper in the u.s. system of government