Staff at Amnesty International are to be balloted this month over strike action, union representatives have said.
The trade union Unite, which represents more than 300 of Amnesty International's 650 employees, confirmed that a ballot would begin next week in response to possible job losses at the human rights organisation.
Amnesty International announced in June that it planned up to 95 redundancies in response to a reported £17m shortfall in its budget.
But it said last week that the number "will not exceed 20".
The ballot will open on 26 September and last until 7 November.
For a strike to be called, 50 per cent of staff need to take part in the ballot and a majority needs to be in favour of such a course of action.
Unite has called on Amnesty International, which is the London-based international secretariat for 50 national sections worldwide, to consider using donations to keep employees in work rather than put them in reserves. Management rejected this.
Alan Scott, regional coordinating officer at Unite, said: "Unite has exhausted all the available dispute resolution options open to it, including meetings at the conciliation service Acas.
"Unfortunately, Amnesty’s management has refused to countenance reducing the amount of money being pumped into reserves in order to save jobs, so members felt they had no option but to ballot for industrial action.
"Amnesty’s management can still have the opportunity to prevent industrial action by tabling proposals that redundancies will be avoided by using a fraction of its reserves."
A spokeswoman for Amnesty International said: "Regrettably we do not have the option to further reduce the level of reserve as it is at the absolute minimum to ensure the fiscal future of the organisation."
She added that the organisation was confident it could further reduce the number of redundancies by redeployment.
"We deeply regret that these redundancies have been made necessary due to harsh financial realities and the need to put the secretariat onto a more stable footing for the future," the spokeswoman said.
"This is a painful and difficult decision, and we will do everything in our power to support affected staff.
"We fully recognise and support Amnesty International employees’ right to strike."
The ballot will open on Thursday 26 September and close on Thursday 7 November. The extended voting period is to ensure that all of the 300-plus Unite members of Amnesty International, including those who work abroad, can participate.