open season on
A period of unrestrained criticism or attack on something or someone, as in During an election year it's open season on all officeholders. This expression alludes to the period during which one may legally hunt or fish. [Colloquial; c. 1900]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.