Although federal judges are the ultimate arbiters of insider trading enforcement, the role of their political ideology in insider trading is unclear. Using the partisanship of judges’ nominating presidents to measure judge ideology, we first document that liberal judges are associated with heavier penalties in insider trading lawsuits than conservative judges. Next, we find that firms located in circuits with more liberal judges have fewer opportunistic insider sales. Cross-sectional analyses show that this deterrent effect is stronger when managers face a higher risk of insider trading lawsuits. Finally, we find that the Securities and Exchange Commission considers judges’ ideology when selecting litigation forums.

We investigate whether judges’ political ideology affects corporate tax behaviors. We find that firms engaging in less aggressive tax planning when Circuit Court judges are more liberal. Cross-sectionally, the deterrent effect of liberal judge ideology is more pronounced for firms that engage in judiciary-sensitive tax strategies, face higher enforcement risk from the Internal Revenue Service (IRS), or have larger reputational costs from tax disputes. Our findings further suggest that liberal judge ideology reduces firms’ R&D investments and market value by constraining tax planning. Overall, our evidence highlights the importance of judge ideology for firm behavior in the context of corporate tax planning.