open up a can of worms
open (up) a can of worms
To initiate, instigate, or reveal a situation that is, will, or is likely to become very complicated, problematic, or have a negative outcome. I worry that trying to tweak the existing system could open up a can of worms that we're not anticipating. The candidate opened a can of worms when he made those inflammatory comments. Now the entire election has been dominated by the topic.
open up a can of wormsdiscover or bring to light a complicated matter likely to prove awkward or embarrassing. informal
1998 New Scientist UN officials readily accept that they have opened a can of worms, and their guidelines will only have an effect, they say, if governments act on them.