KRAKOW, Poland — The front page of Poland’s leading newspaper featured on Monday an open letter from three former presidents warning that the new right-wing government’s actions were threatening the country’s democracy.

Lech Walesa, the 1983 Nobel peace laureate whose Solidarity movement led Poland’s emergence from Communism, was joined by Aleksander Kwasniewski, president from 1995 to 2005, and Bronislaw Komorowski, president from 2010 until last year, in calling on Polish citizens to “defend democracy” in their letter, published by Gazeta Wyborcza. The three former presidents and seven opposition politicians and activists also warned the leaders of the ruling Law and Justice party that “those guilty of violating the Constitution shall bear responsibility.”

The right-wing Law and Justice party has been embroiled in controversy almost from the moment it took power in October after a decisive win in parliamentary elections that ended eight years of rule by the center-right Civic Platform. Much of the criticism has come over the new government’s moves to weaken Poland’s constitutional court, which have earned rebukes from European leaders as the country is preparing to host the annual summit meeting of leaders from the North Atlantic Treaty Organization in July.

The European Parliament voted this month on a resolution that accused Poland’s government of undermining the country’s democracy, passing the issue along to the European Council for further action.