Iowa Code § 573.15: Claim against retainage or bond.

1. A person, firm, or corporation that has performed labor for or furnished materials, service, or transportation to a subcontractor shall not be entitled to a claim against the retainage or bond under this chapter unless the person, firm, or corporation that performed the labor or furnished the materials, service, or transportation does all of the following:

a. Notifies the principal contractor in writing with a one-time notice containing the name, mailing address, and telephone number of the person, firm, or corporation that performed the labor or furnished the materials, service, or transportation, and the name of the subcontractor for whom the labor was performed or the materials, service, or transportation were furnished, within thirty days of first performing the labor or furnishing the materials, service, or transportation for which a claim may be made. Additional labor performed or materials, service, or transportation furnished by the same person, firm, or corporation to the same subcontractor for use in the same construction project shall be covered by this notice.

b. Supports the claim with a certified statement that the principal contractor received the notice described in paragraph “a”.

2. This section shall not apply to highway, bridge, or culvert projects as referred to in section 573.28.