The automatic annual increases are usually based on a figure agreed for local authorities. Last year this was 2.45 per cent.
Richard Cove, executive director of HR at the charity, wrote to employees in April saying that in the current climate the charity should be "managing our own pay decisions rather than relying on third-party negotiations we cannot participate in and which take no account of charity sector issues".
Cove said the charity intended to return to salary reviews and incremental progression from the 2010 review.
Rachael Maskell, national officer for the not-for-profit sector at Unite, said: "After consultation with our legal team, we concluded that suspending incremental pay increases would be a breach of contract and asked the charity to reconsider its proposals."
Cove told Third Sector last week: "We hope to reach a mutual agreement soon."