MOSCOW (Reuters) – Russia is preparing retaliatory measures against Poland to punish it for what Moscow says is an illegal and immoral plan to tear down Soviet-era World War Two monuments, an ally of President Vladimir Putin said on Wednesday.

Polish President Andrzej Duda on Monday approved amendments to a law banning the promotion of communism and ordering the removal within a year of Soviet statues, including those that commemorate the Red Army.

Valentina Matviyenko, speaker of the Russian upper house of parliament and a close Putin ally, strongly criticized the move on Wednesday and said the Russian Foreign Ministry was drawing up retaliatory “measures,” Russian news agencies reported.

The dispute centers on the two countries’ differing interpretations of history.

Russia says the Polish move spits in the faces of the more than 600,000 Soviet troops who lost their lives liberating Poland from the Nazis.

But many Poles today say they view the Soviet troops as occupiers, not liberators. Poland was under Soviet control for over four decades after the Second World War and the last Russian soldiers only left in 1993.

When asked about Matviyenko’s comments, the Russian Foreign Ministry referred Reuters to a statement it issued on Tuesday which said Poland’s actions would trigger “consequences” for Warsaw.

The statement said the Polish move violated a 1992-1994 Russo-Polish agreement in which Poland had pledged to protect such monuments.

“The Polish authorities understand very well what a serious insult they are delivering to the Russian people and the people of countries that used to be part of the USSR,” the statement said. “Nevertheless, in Warsaw they are consciously going ahead with this outrageous provocation.”