Tom Stratmann and J.W. Verret have written this article for the Journal of Law and Economics. Here is the abstract:
The US Supreme Court case Citizens United v. Federal Election Commissionsignificantly altered the regulatory landscape for corporate political activity by permitting unlimited corporate expenditures by independent politically active groups. This paper uses that event to determine the impact of corporate political activity on the stock prices of those firms that are most likely to utilize these new opportunities for political engagement. Our findings show that corporate political activity enhances shareholder wealth, particularly in firms that are small to medium sized, firms that spend relatively less on lobbying, and firms operating in more heavily regulated industries.