Proxy-advisory firms, under scrutiny in Washington over the weight given to their corporate-policy guidance, aren’t giving companies enough time to respond to voting recommendations that oppose management’s plans, a report released Monday contends.

And investors that typically follow the firms’ suggestions on matters from executive pay to environmental issues aren’t always analyzing them closely before before voting, according to the study, which was commissioned by the non-profit American Council for Capital Formation. Advisers for the group, which receives most of its funding from outside contributions, include former Democratic Sens. Max Baucus and Joe Lieberman, former Secretary of State George Shultz, and Mark Weinberger, chief executive officer of Ernst & Young.