The Green Party is to take control of Brighton and Hove City Council after three Labour councillors resigned, with two of them accused of anti-Semitism.
Kate Knight and Nichole Brennan both stood down on Tuesday.
Brighton and Hove City Council said a number of complaints had been made to the national Labour Party over Ms Knight’s Facebook activity.
The latest resignations come five days after Anne Pissaridou also resigned over social media posts.
Labour now has 18 seats, compared to the Greens’ 19 councillors.
Brighton Council would give no more information on the circumstances surrounding Ms Brennan’s resignation.
The Green Party said: “It is clear neither party can claim a majority to lead our city alone.
“We understand Labour are still divided and that some councillors have made clear their unwillingness to support a Green-led council. Residents will have no time for the luxury of parties debating ‘seizing power’.
“Greens are keen to engage with our party membership, the Labour group and all partners to find the best way forward.”
‘Shame on the party’
In a statement, the council’s Labour group said: “It is only right that Labour step aside and allow the Greens to form a new administration. This is in the interest of democracy and in the best interests of the city.”
The council’s former Labour leader, Nancy Platts, said it brought shame on the whole Labour Party to see Ms Knight’s posts.
“On behalf of the Labour group, I am truly sorry to the Jewish community for the hurt these posts have caused.”
She said the Labour group would establish a code of conduct for all councillors to include an emphasis on social media and the importance of recognising anti-Semitic posts.