Iowa Code § 26.16: Prequalification requirements prohibited.

A governmental entity shall not by ordinance, rule, or any other action relating to contracts for public improvements for which competitive bids are required by this chapter impose any requirement that directly or indirectly restricts potential bidders to any predetermined class of bidders defined by experience on similar projects, size of company, union membership, or any other criteria. However, a governmental entity shall require nonresident bidders to comply with section 8A.311B, subsection 4.