Uniform Commercial Code (UCC): Primary legislation governing sales and commercial transactions, particularly Article 2 which deals with sale of goods. Essential for establishing basic contract modification rules.

State Contract Laws: State-specific contract regulations that may affect how contract modifications and extensions are handled in the particular jurisdiction.

Statute of Frauds: Legal requirement that certain contracts and their modifications must be in writing and signed to be enforceable.

Real Estate Settlement Procedures Act (RESPA): Federal law governing real estate transactions, including requirements for settlement services and disclosures if the contract involves real property.

Truth in Lending Act (TILA): Federal regulation requiring disclosure of key terms and costs in transactions involving consumer credit, relevant if the extension involves financing terms.

Federal Trade Commission Regulations: Federal consumer protection rules that may affect contract terms and required disclosures, particularly in consumer transactions.

State Consumer Protection Statutes: State-specific laws protecting consumer rights that may impact how contract extensions must be structured and documented.

Magnuson-Moss Warranty Act: Federal law governing consumer product warranties, relevant if the original sale and purchase contract includes warranty terms that need to be extended.

Statute of Limitations: Time limits set by state law for enforcing contract rights or bringing legal actions, which may affect extension terms.

State Recording Requirements: Legal requirements for recording or filing contract modifications, particularly important for real estate transactions.

Notarization Requirements: State-specific rules regarding when contract modifications must be notarized to be legally valid.