Victim Support chief executive Katie Kempen highlighted the Labour government's manifesto pledge to halve violence against women and girls within a decade.
“This unprecedented cut to victims' services funding, combined with the increase in National Insurance contributions, is devastating for our services," she said.
"Unless this decision is reversed, the stark reality is that people who have experienced the shock and trauma of crime, including domestic-abuse and sexual-violence survivors, will have to go without vital support."
As well as reversing the cut, the charity wants the funding raised to cover the National Insurance rises.
In recent weeks, the government has made a number of pledges to better protect crime victims, including:
The 4.2% cut is to the Ministry of Justice (MoJ) funding from which police and crime commissioners in England and Wales commission practical and emotional support services for victims, based on their assessment of local need.
The separate Rape and Sexual Abuse Support Fund will remain at £21m for 2025-26, with no funding increase to account for inflation, while the MoJ's s overall budget for the same time period has risen by 4.3% in real terms.
Victims Minister Alex Davies-Jones said: “This government inherited a criminal-justice system under immense pressure and a black hole in the nation’s finances.
“We must now make difficult decisions to ensure we can deliver the justice victims deserve, through our courts and across the system.
"By protecting our support for victims of sexual violence and domestic abuse, we are ensuring help is available to survivors of these awful crimes as they seek to rebuild their lives.”