48 CFR §28.106-5

1. (a)When any contract is modified, the contracting officer shall obtain the consent of surety if—
   1. (1)An additional bond is obtained from other than the original surety;
   2. (2)No additional bond is required and—
      1. (i)The modification is for new work beyond the scope of the original contract; or
      2. (ii)The modification does not change the contract scope but changes the contract price (upward or downward) by more than 25 percent or $50,000; or
   3. (3)Consent of surety is required for a novation agreement (See subpart 42.12).
2. (b)When a contract for which performance or payment is secured by any of the types of security listed in 28.204 is modified as described in paragraph (a) of this subsection, no consent of surety is required.
3. (c)Agencies shall use Standard Form 1414, Consent of Surety, for all types of contracts.