Runwood Homes, which employs nearly 300 people at seven older people's homes across Doncaster, announced proposals in April to cut pay and change working conditions for staff who had transferred from Doncaster Council two years ago.
The GMB union says the worst-hit workers would see their wages slashed by 24 per cent, losing up to £900 a month, under changes which the company says are needed to keep the homes open.
The GMB today said it was left with no option but to ballot members over industrial action after talks with Runwood broke down.
Deanne Ferguson, the union's regional organiser, said: "The proposed changes to our members' pay, terms and conditions are some of the most brutal attacks I have ever seen on already low-paid workers across Doncaster."
She claimed members 'simply cannot afford to live decently' should the proposals go ahead in their current form, and accused Runwood of refusing to respond to alternative proposals put forward by the union.
Runwood, which the GMB described as one of the UK's fastest-growing care providers, last year increased its turnover by nearly 11 per cent to £117.4 million, recorded a £5.5m profit and paid £7m in dividends.
A spokeswoman for the firm said it was consulting staff and unions over the proposed changes, and no firm decisions had been made.
"We are seeking to make these changes to protect the opportunities these homes offer our staff and residents while at the same time recognising the homes are not sustainable," she added.
"With material financial losses posted for this region and a forecast showing this trend is set to continue, the existing operating model must be changed to ensure longevity of these homes."
She added that Runwood has 'exciting plans' to extend the service it provides in Doncaster but was focused for now on securing the 'future financial stability' of its existing homes in the area.
The seven homes affected, which were sold by Doncaster Council two years ago, have 274 beds between them.
They are: Gattison House, Rossington; Owston View, Carcroft; Oldfield House, Stainforth; Rose House, Armthorpe; Plantation View, Cantley; Stenson Court, Balby and Rowena House, Conisbrough.