Mo. Rev. Stat. § 436.315: Withholding of retainage prohibited, when.

A contractor shall not withhold from any subcontractor any retainage in excess of the retainage withheld from the contractor by the owner for the subcontractor's work, unless the subcontractor's performance is not in accordance with the terms of the subcontract, in which case, subject to the terms of the subcontract, the contractor may retain additional sums to ensure the subcontractor's satisfactory performance of the subcontract.