Contracts with public bodies are enforceable only if made by someone with authority, and the rules are stricter than in private dealings.
Actual authority only. Apparent authority generally does not bind a public body. A person dealing with a public official is charged with knowledge of the limits on that official’s authority, which is a rule that surprises contractors regularly.
Sources of authority. Statute, charter, ordinance, and a resolution of the governing body. Delegations must themselves be authorised.
Consequences of an unauthorised contract. Frequently void rather than voidable, with no recovery even in restitution in many states, on the reasoning that permitting quantum meruit would defeat the protective purpose of the requirements.
Ratification. A public body may ratify an unauthorised act it could have authorised, by formal action, provided the original defect was not one the body could not have cured — such as a failure to comply with mandatory bidding.
Practical protection for contractors. Obtain a certified copy of the authorising resolution before performing, confirm the appropriation, and never proceed on a verbal instruction to perform additional work.
Practical protection for public bodies. A signature authority policy, a requirement that contracts above a threshold be reviewed, and training for department heads.