The popular Onet website reported in an investigative piece on Monday that Łukasz Piebiak was the brains behind a campaign whose aims included discrediting the head of Poland’s largest judges’ association.
Piebiak denounced the claims, saying he would sue Onet for lying and “spreading slander.”
Explaining his decision to quit, he added: “I do not want the slander against me to become an excuse for attacks on changes to the judicial system that millions of Poles waited for."
Poland's governing Law and Justice party, which came to power in late 2015, has argued that sweeping changes are needed to reform an inefficient and sometimes corrupt judicial system tainted by the communist past.
Amid claims that the country’s ruling conservatives had undermined the independence of judges, the European Commission in December 2017 took the unprecedented step of triggering Article 7 of the EU Treaty against Poland.
The EU’s executive arm last month launched the second stage of an infringement procedure against Warsaw over new disciplinary rules for judges.
The claims of the alleged hate campaign against judges come as Poland counts down to parliamentary elections in October, with the governing Law and Justice party bidding for a second term in power.
Poland’s prime minister argued in January that some of the legal changes made by his government have met with criticism abroad because they are not understood in Western Europe.