Left-wing Meretz led by newly-elected leader Nitzan Horowitz, and the newly-formed Democratic Party led by former Israeli prime minister Ehud Barak said on Thursday that they had built up an alliance called the Democratic Camp, Presstv Reported.
Such a union is not likely to pose a serious threat to Netanyahu’s Likud but it could act as a catalyst for further mergers among smaller parties, fractioning both the left-wing and right-wing vote.
Netanyahu won a fifth term in office in the April elections after his right-wing Likud Party won 35 of the Knesset's 120 seats. He had until 21:00 GMT on May 29 to form a cabinet that controlled at least 61 seats in the 120-member parliament.
But despite weeks of negotiations, he failed to bridge the gap between secular and religious allies.
Late in May, Israeli legislators voted by 74 to 45 to dissolve the Knesset, setting the regime on the path to a snap election due to take place in September 17.
Meretz barely passed the threshold in April snap elections. The Democratic Party, for its part, would not make it into the Knesset through the September’s vote, opinion surveys show.
“The initiators of the union believe that forming the Democratic Camp is the first and crucial step in the mission of bringing Israel back on track,” said a statement from the alliance on Thursday.
The union was facilitated by Stav Shaffir of Labor, who will win the second place on the list. Labor head Amir Peretz, who will receive the first place, rejected the notion of joining forces with Meretz.
The alliance will be led by Horowitz, with Barak taking the tenth place on the list.
On July 18, Gesher Party chair Orly Levy-Abekasis and Peretz also announced their joint run in the September election.
Netanyahu, whose fifth term in office has been jinxed, vowed at the time that his conservative party would win the new vote.
His coalition talks reached a stalemate over disagreements between ultra-Orthodox parties and Yisrael Beiteinu, a secular right-wing party led by former minister of military affairs Avigdor Lieberman, on a military conscription bill.
Following the Knesset decision in late May, Lieberman wrote on his Facebook page that Likud held responsibility for the repeat election because of its refusal to vote on a bill to draft the ultra-Orthodox.
Netanyahu, however, said Lieberman misled his voters and was dragging the entire Israel into a new election "after he was the cause of the previous one too, just because he wants a few more votes, which he won’t get. It’s just unbelievable."