It comes as figures reveal that early intervention schemes to help young mental health patients have been reduced over the past 12 months.
Mental health trusts are being asked to save almost 20% more from next year's budgets than hospitals.
NHS England says it has put procedures in place to ensure mental and physical health are treated equally in future.
The Mental Health Foundation, Rethink Mental Illness, Mind, the NHS Confederation Mental Health Network and the Centre for Mental Health and the Royal College of Psychiatrists have released a letter on Wednesday warning that planned cuts for next year will put lives at risk as the system is already underfunded.
One charity says half of early intervention programmes aimed at young people have been cut in the past year.
Early intervention schemes are intended to reduce suicide rates, prevent patients from becoming more ill and to keep patients out of hospital and in work, and were praised last week by the chief medical officer for England.
Sean Duggan, chief executive of the Centre for Mental Health, said early intervention programmes were "very good value for money" and the prospect of budget cuts was "very worrying".
"Early Intervention in Psychosis services are known to be highly effective in helping young people to negotiate their first episode of psychosis", he said.
"They offer hope of a brighter future by helping young people to stay in education, to get and keep work, and to support their physical health."
He described the cuts as a "false economy".
"They save the NHS £9 and the wider economy another £9 for every £1 invested in them."
He added that the cuts meant young people are now facing delays in getting help.
A separate report from the charity Mind shows that mental health patients are losing social care support in greater numbers than elderly or physically-disabled people.
The charity points to research by the London School of Economics which suggests 30,000 people with mental health problems have lost their social care support since 2005, following a £90m shortfall in funding.
It also found that one in three local authorities in England halved the number of people with mental health problems receiving social care support.
In a statement, NHS England said it had been "working solidly in its first year now to ensure that mental health no longer inhabits the silo that existed in the old system but is fully embedded in all the work we're doing to deliver outcomes and high quality care".
Six mental health organisations in England are warning that NHS cuts are putting lives at risk.