Guinness, the famous Irish stout, is being sued because THE BEER IS ACTUALLY MADE IN CANADA!
Kieran O'Hara is a local beer drinker from Massachusetts now gunning for Guinness, claiming the beer maker is duping millions of beer enthusiasts.
According to the docs -- obtained by TMZ -- O'Hara claims Guinness plasters a misleading label on every bottle of Guinness Extra Stout that makes people think it's a 100% Irish beer -- with ONLY a teeny tiny disclosure on the back of the bottle saying it's ACTUALLY made in Canada.
O'Hara isn't just in it for himself -- he's trying to put together a class of other Guinness drinkers who thought they were drinking an authentic Irish beer.
We reached out to Guinness for comment ... so far, no word back.
Our guess? If O'Hara wins, he'll celebrate with a cold pint.