This study estimates the policy effects of the Pre-Bid Screening Scheme introduced by the Seoul Metropolitan City and Gyeonggi Province to restrict the entry of construction firms that fail to meet registration requirements—such as paper companies—into the public construction bidding market. Using the number of bidders as a proxy for the tightening of market entry barriers and applying a Difference-in-Differences approach, we find that the scheme led to an average reduction of 31.3% in Seoul and 10.7% in Gyeonggi Province. A period-specific analysis shows that the policy effects strengthened as the scheme was reinforced, and it did not distort the market’s competitive price adjustment mechanism.