The union giant has warned homelessness services such as women's refuges and youth shelters will be hit hard by the axing of a $115 million program to address the rising numbers of homeless.

It has also criticised a $40 million cut to community legal centres, to take effect next year, and a reduction in support for mental health services, including Headspace's youth psychosis program.

Australian Services Union NSW/ACT acting secretary Judith Wright said the impact would be felt by the most disadvantaged people in the country.

"This budget is an attack on Australia's most vulnerable," she said.

"The damage these cuts will cause will be horrific. These are the jobs of people who work in the community sector supporting some of our most vulnerable young people and women leaving violence."

Peak body Homelessness Australia also criticised the decision to cease the National Partnership Agreement on Homelessness from 2017.

Michael Coffey, chief executive of youth homelessness service YFoundations, said the $115 million funding supported 80,000 people a year.

"Services are at breaking point and communities across Australia will continue to see more and more people turned away from services and on the streets," he said.

Mission Australia chief executive Catherine Yeomans expressed concern that the budget failed to address the lack of social and affordable housing.

"A crucial factor in the rising rates of homelessness is the lack of affordable housing in cities and towns across the country," she said.

"Again, the government has missed the opportunity of the budget to provide any measures facilitating the growth of necessary social and affordable housing."