Martin Glvac, leader of the Bratislava chapter of Fico's Smer party, is the highest-ranking individual to resign over contacts with politically-connected entrepreneur Marian Kocner.
Slovakia's parliament deputy speaker resigned on Thursday over contacts with a businessman charged with ordering the murder of a journalist last year that sparked mass protests which ousted then Prime Minister Robert Fico.
Martin Glvac, leader of the Bratislava chapter of Fico's Smer party, is the highest-ranking individual to resign over contacts with politically-connected entrepreneur Marian Kocner, whose extensive reach within the state was revealed by the investigation into the killing.
Last month, police completed the initial phase of the case, seen as a test of Slovak judicial independence. They charged Kocner and three others with the murder of Jan Kuciak, who covered corruption in the EU country, and his fiancee at their home outside Bratislava last February.
Kocner and two alleged accomplices have pleaded not guilty while the fourth suspect has confessed to the shooting. A fifth man has confessed to facilitating the killing and made a plea deal with prosecutors to act as a witness in the trial.
Revelations of links between Kocner and security officials that were exposed during the investigation have led to more resignations in recent weeks.
Glvac admitted to having known Kocner but denied any wrongdoing. He said on Facebook that he expected several other political figures who had had contacts with Kocner, including leaders of some opposition parties, to resign as well.
General prosecutor Jaroslav Ciznar last month temporarily suspended his predecessor, prosecutor Dobroslav Trnka, after a video leaked to the Czech website Investigace.cz showed Kocner installing a hidden camera in Trnka's former office.
Prosecutors said in August they had extracted tens of thousands messages from Kocner's phone, containing communication with "representatives of state bodies and the justice system".
Slovak media published parts of the messages, leading to resignations of a deputy minister, two prosecutors and a judge.
Although Fico resigned over the case last year, his ruling three-party coalition has survived, led by his hand-picked successor Peter Pellegrini. The case could have a major impact in a general election scheduled for February 29.