Iowa Code § 573.3: Bond mandatory.

1. The obligation of the public corporation to require, and the contractor to execute and deliver said bond, shall not be limited or avoided by contract.

2. A public corporation, with respect to a public improvement which is or has been competitively bid or negotiated, shall not require a contractor to procure a bond, as required under section 573.2, from a particular insurance or surety company, agent, or broker.