More than 450 members of union Unite are balloting on strike action over management proposals to scrap incremental pay rises, increase working hours from 35 to 37.5 and make redundancies.
Shelter chief executive Adam Sampson said changes to the government's competitive tendering system meant the charity had been forced to make changes.
Contracts
"We cannot afford to lose these contracts or we will be failing the hundreds of thousands of people and families we help every year. The status quo is not an option and we need to act now or it will be too late," he said.
Unite national secretary Doug Nicholls said: "Shelter's arguement is with the government and the Legal Services Commission, which is driving down services by cutting funding with little regard to the effect on quality of service. We will happily join with Shelter's management in lobbying to reverse that injustice. But we are not prepared to allow our dedicated members to be forced to subsidise the charity's operation through cuts in pay and conditions, and to damage the service we provide."