Iowa Code § 539.2: Assignment prohibited by instrument.

When by the terms of an instrument its assignment is prohibited, an assignment thereof shall nevertheless be valid, but the maker may make use of any defense or counterclaim against the assignee which the maker may have against any assignor thereof before notice of such assignment is given to the maker in writing. In case of conflict between this section and section 554.5112, 554.5113, 554.5114, 554.9404, or 554.9405, section 554.5112, 554.5113, 554.5114, 554.9404, or 554.9405 controls.