The action follows the Council's decision to slash funding to service-delivery groups in its budget for the financial year beginning April.
If implemented, the cuts will endanger the future of 78 not-for-profit organisations and more than 400 voluntary sector jobs.
Leicester City Council has so far refused to respond to a letter written by the Public Law Project, a London-based organisation that advises on public law issues, and demands that a three-month consultation process with service delivery groups should precede any decision on cuts.
Voluntary Action Leicester, one of the organisations working with the Public Law Project, says that affected charities are prepared to take the matter to a judicial review and seek an injunction, forcing the council to freeze any decision to make cuts until a proper consultation has taken place. "We have spent the past three years building up a modern infrastructure for the voluntary sector in the city in line with government aspirations," said Kevan Liles, chief executive of Voluntary Action Leicester. "These proposals will devastate what we have done."
Leicester City Council's decision to make the £2m cuts was announced in the same week that Chancellor Gordon Brown told delegates at the NCVO conference that he planned to extend volunteering schemes.
Leicester Volunteer Centre, which Liles' organisation funds through its grant from the council, faces an £80,000 shortfall if the funding is withdrawn.
"It's a real possibility that it will close," said Liles. "The volume of people the centre attracts will not abate, and that could overwhelm an organisation that is to receive a fifth of its previous funding."
The cuts were mooted in January when the council said it would save a fifth of its £10m budget shortfall by reducing contributions to the voluntary sector.
After consulting on the proposals, councillors have decided to reprieve 10 voluntary organisations, including the YMCA, the Alzheimer's Society and Rape Crisis. However, the concessions amount to only £169,000.
Council leader Roger Blackmore said Leicester traditionally gave far more to the voluntary sector than other authorities. He added there was a problem with funding charities that do "more or less the same thing".
"A new administration took over in May and we promised new budgets to get the whole city on a sound financial footing," he said.