Unilateral modifications exercise a right already in the contract. You are not asking for permission - you are telling the contractor you are exercising a right. Understanding this distinction is fundamental to contract administration.
Unilateral Modifications (FAR 43.103(a)) are signed by the Contracting Officer only. They exercise a right the Government already has under the contract. The contractor's signature is not required because the clause gave the Government that authority at award. Common authorities include the Changes clause, Options clause, Government Property clause, and Termination clauses.
Bilateral Modifications (FAR 43.103(b)) are signed by both the Contracting Officer and the Contractor. Also called "supplemental agreements," these are used when both parties must agree to the change - things like negotiated equitable adjustments, definitization of letter contracts, changes the contract doesn't already authorize, and no-cost modifications the contractor agrees to.
| Feature | Unilateral | Bilateral |
|---|---|---|
| Signatures | Contracting Officer only | Both CO and Contractor |
| Contractor consent | Already given at award (via clause) | Required for this specific change |
| Authority source | Specific contract clause | Negotiated agreement |
| Legal basis | FAR 43.103(a) | FAR 43.103(b) |
| Time to execute | Fast - no negotiation needed | Slower - requires negotiation |
| Common use cases | Options, Changes, Stop-work, Termination | Equitable adjustments, scope additions, definitization |
| Can contractor refuse? | No - Government has the right | Yes - both parties must agree |
Use Unilateral when:
Use Bilateral when:
Think of it this way: if you buy a car with a warranty, the warranty clause gives you (the buyer) rights to service or replacement. When you use that warranty, you don't need the dealer's permission again - you're exercising a right the dealer already gave you at sale. The dealer can't refuse. Same principle applies here. The contractor signed the contract knowing it contained an options clause, a changes clause, a termination clause, etc. They consented to those clauses. When you exercise those rights, you're not asking for new permission.
This is why it's critical to identify the correct clause authority BEFORE issuing a unilateral modification. If you don't have a clause that grants you the right, you can't use a unilateral mod. You'd have to negotiate bilaterally.
You are a contracting specialist managing a janitorial services contract. The original contract was for 2 years, with 3 one-year options. You've been directed to exercise the first option year.
Your steps:
Outcome: The contract period is extended. Unilateral, fast, no negotiation needed because both parties already agreed to the option at original award.
The COR now wants to add pressure washing to the same janitorial contract. This was not in the original scope.
Your analysis:
Key learning: Sometimes the question isn't "unilateral or bilateral?" but rather "Is this change within scope such that the Changes clause allows it?" Get that question right first, then the unilateral vs. bilateral decision becomes clear.
Unilateral modifications exercise a right the Government already has. The contractor already agreed to that right when they signed the contract. Use them when you can cite a specific clause that grants you authority. They're fast and efficient.
Bilateral modifications require new agreement from both parties. Use them for changes the contract doesn't authorize, or when you need the contractor's consent. They're slower but necessary when you don't have unilateral authority.
Click any clause below to expand and see what right it grants, when to use it, and whether the contractor has recourse.