The unions have claimed that Action for Children will impose a 1 per cent pay award for 2015/16 with no cost-of-living rise for 40 per cent of its 5,000 employees. Unite has more than 400 members at the charity; Unison has 700.
The unions have said that Action for Children also intends to remove contractual pay increments for new starters, refuse to pay the UK living wage of £8.25 – £9.40 in London – and will cut mileage rates on claims for travel expenses.
Unite and Unison have argued that, despite the pay reforms, the number of senior executives earning more than £70,000 at the charity has increased from 16 to 21 and another member of staff is on £120,000 a year.
The unions said that the charity’s chief executive, Sir Tony Hawkhead, had stated his intention to impose the new pay offer, which was rejected by both unions’ membership in consultative ballots.
The unions claim the charity refused to involve the conciliation service Acas in the dispute, although Hawkhead said in a statement that he "welcomes the involvement" of services such as Acas.
Action for Children had an income of £173.1m in the year to 31 March 2015, £6.6m less than in the previous financial year, according to figures on the Charity Commission website. The charity spent £159.9m in 2014/15.
Hawkhead said the decision to make changes to pay and conditions was a result of a "six-month-long series of extensive discussions with both unions since April 2015" and the charity had "sought to use a finite sum in the fairest way".
He said: "Our primary focus is always to ensure that our resources are directed in the best way possible so that we can continue to support some of the most vulnerable people in society.
"The sector is seeing unprecedented demand for front-line services. The effects of government spending cuts are also taking hold in communities across the country, meaning that the voluntary sector must play an increasingly important role."
Simon Watson, national voluntary sector officer of Unison, said: "Action for Children claims it is strapped for cash, yet it has managed to find the money to increase the number of its highest-paid managers. Meanwhile, staff haven’t had a pay rise in six years.
"The decision to move to a ballot for action is always a reluctant one, but despite over a year of negotiations the charity still refuses to see sense. As a result many employees are being forced into extreme hardship. Some have to use the same foodbanks as the families they are trying to help. It's still not too late to prevent action, and we hope the charity uses the coming weeks to think carefully about its next steps."
Sally Kosky, Unite national officer for the not-for-profit sector, said the average pay for staff at Action for Children had fallen by 52 per cent in real terms since 2010/11.
"The management is behaving in a high-handed manner, trying to bulldoze a wholly inadequate pay offer onto our members and refusing point-blank to involve Acas in the dispute," she said.
"Just because people work for a charity, they don’t deserve the prospect of poverty wages.
"The organisation has a healthy surplus and some of these reserves should be used to fairly reward its hard-working staff."
The ballots by the two unions will open tomorrow and close on 16 February.