can of worms

noun

1. Informal. a source of many unpredictable or unexpected problems:

   Buying a company we know nothing about would be opening up a whole new can of worms.

Word History and Origins

Origin of can of worms¹

First recorded in 1965–70

Idioms and Phrases

A complex unexpected problem or unsolvable dilemma, as in Tackling the budget cuts is sure to open a can of worms . This expression alludes to a container of bait used for fishing, which when opened reveals an inextricable tangle of worms. [1920s]

Example Sentences

Mistakes, yes – but honest ones, only for the emergence of the Coote video to reopen a very large can of worms, presenting a crisis for Webb and PGMOL.

From BBC

Supervisor Hilda Solis, the other no vote on the county board, agreed, saying a ruling in Grants Pass’ favor would “open a can of worms.”

From Los Angeles Times

Could allowing people to sue for these kinds of mob-like statements open a proverbial can of worms?

From Salon

But that opens up a further can of worms.

From BBC

"They may yet change it but I wouldn't expect that as that would open a can of worms and they have very much seen what happens from overseas examples with other royal families."

From BBC