Allowing Israel Beiteinu leader Avigdor Lieberman (read his JPost blog) to join Prime Minister Ehud Olmert's coalition is my only regret, Labor chairman Amir Peretz told a rally of supporters on Saturday night. Peretz said he did not regret accepting the Defense portfolio because of his impact on socioeconomic issues in the army and his desire to prove that a minister who is not a former general could succeed in the post. However, he said he did regret not fighting Labor ministers who insisted on remaining in the cabinet when Lieberman joined. "My only political decision that I regret is not causing a coalition crisis over Lieberman," Peretz told the crowd. "That's where I think I made a big mistake. I shouldn't have let [Lieberman's joining happen]. "Even if I would have been a minority in the party and even if I would have been the only one to vote against it in the government." Peretz also announced at the event that he planned to sue Ma'ariv for suggesting in a headline on Friday's front page that he had ties to organized crime, because he attended the same wedding as two criminals. In weekend interviews, Peretz lashed out at his challenger for the Labor leadership, former prime minister Ehud Barak. Peretz questioned whether Barak was more loyal to Olmert than Labor and suggested that he did not even vote for Labor in the last election. "Not to be there for the election, not to help the party and now to seek the crown - there has to be a limit even for those who have no limits," Peretz told Yediot Aharonot. "This time, this candidate crossed the line." Referring to Barak's consulting and public speaking business in the United States, Peretz accused Barak of "thinking that he can use Labor as a toy that he can play with when he comes back to his homeland on vacation." Neither Lieberman nor Barak responded to Peretz's comments. Labor leadership candidate Ophir Paz-Pines, who quit the government to protest Lieberman's addition, responded to Peretz by saying: "Peretz's behavior on the Lieberman issue proved his lack of leadership and ideology. He zigzagged, broke his promises and made Labor spare change in the government. For this reason alone, he should give back the keys and quit the Labor leadership."