In a postal ballot, members of the GMB general union at the Regent's Park site have added their voice to calls from the society's members for the resignation of all officers and managers involved in the June decision to close the loss- making zoo at the end of September.
Three-quarters of the 80 GMB members took part in the ballot, and every vote was cast in favour of a resolution demanding a clean sweep of the society's leadership, apart from three spoilt papers.
But the council, headed by Field Marshal Sir John Chapple, is organising a counter-attack against the society's members - known as fellows - who want new blood.
About 200 fellows last month voted in favour of keeping the 166-year-old zoo open as well as for resignations. The council's response is to hold a postal ballot of the entire fellowship, which is just over 2,000 strong. It is asking them for a vote of support; if it gets one, it can use it to claim that the fellows attending the meeting were a dissident minority.
Alison Cobb, secretary of the Reform Group of fellows which has led opposition to the council and management, said: 'The fellows who care, the ones in touch with the zoo, are those who came to the meeting.
'The council is now trying to get the support of the less informed, more out of touch fellows but the vote at the special general meeting is the one that is valid.'
While the arguments continue, the zoo is in limbo. Officially it is due to close in just over six weeks, but this is unlikely. A surprise gift of pounds 1m from the Emir of Kuwait could allow it to struggle on until next summer.
Yet it appears as far as ever from securing the income needed to give it a long-term future. The number of visitors has risen in the past few months, boosted by the publicity about its impending closure, yet there are still not enough.
The zoo is assessing possible rescue bids from the private sector and planning a Jumbo Weekend, based around its Asian elephants and their conservation in the wild, on 26 and 27 September.