I'm guessing this is to do with the
Constitutional Court crisis in Poland? Not something I'd heard about before, but interesting stuff. I think this is the key issue based on the press release: "This crisis has only got worse over the last months. Now, the Constitutional Court is under the political control of the ruling party, constitutionality of laws cannot be checked and ensured any more".
The government isn't recognising various decisions made by the Constitutional Court and is trying to limit its power, from what I can gather from a very brief read. Seems very reasonable that Guy Verhofstadt should call for action.