WARSAW — It may have been a political protest, but it came across like a death threat: Pictures of six Polish politicians were strung from a makeshift gallows in a public square in the southern city of Katowice.

The politicians, all members of the European Parliament and of the opposition party, Civic Platform, had recently voted in favor of a resolution that could potentially lead to stripping Poland of voting rights in the European Union for violating the common values of the bloc, including the rule of law.

The resolution was the latest instance in which the European Union has clashed with the increasingly authoritarian right-wing government in Poland, over such areas as immigration, judicial independence, press freedom and even logging in a primeval forest.

But the images of hanged politicians, and the implication that they were traitors to Poland, have raised haunting questions in this country, which suffered from fascism and communism in the 20th century and was the site of numerous atrocities, including the mass murder of Jews.