Rape victims are being told they must hand over their mobile phones to police or risk prosecutions against their attackers being dropped.
At least two complainants are planning a legal challenge against new consent forms which ask permission to access messages, photographs, emails and social media accounts.
The forms have been rolled out across the 43 forces in England and Wales after a string of rape and serious sexual assault cases collapsed when crucial evidence emerged at the last minute.
Police and prosecutors say they are an attempt to fix a gap in the law which means police cannot currently force complainants or witnesses to disclose their phones, laptops, tablets and smart watches.
But privacy campaign group Big Brother Watch branded the move akin to a "digital strip search" and said "treating rape victims like suspects" could deter people from reporting crimes.
Rape survivor and activist Winnie M Li told Sky News it was wrong to take away a victim's phone at such a vulnerable time and that analysing its contents is "still not going to provide evidence on whether or not a rape was committed".
"At the same time, it may provide certain kinds of messages or insights into her character that the defence can then use against her," said Ms Li.
"I think to require a rape victim to give up her privacy at a time when she's already very vulnerable is doing a huge disservice to rape victims and failing to understand what they're going through."
The form states: "If you do not provide consent for the police to access data from your device you will be given the opportunity to explain why.
"If you refuse permission for the police to investigate, or for the prosecution to disclose material which would enable the defendant to have a fair trial then it may not be possible for the investigation or prosecution to continue."
Director of Public Prosecutions Max Hill said digital devices will only be looked at when it forms a "reasonable line of enquiry" and only "relevant" material will go before a court if it meets "hard and fast" rules.
In the lead-up to trials, police and prosecutors are required to hand over relevant material that can undermine the prosecution case or assist the defence.
The procedure came under sharp focus in 2017 after a string of defendants had charges of rape and serious sexual assault against them dropped when critical material emerged as they went on trial.
They included student Liam Allan who was accused of rape before his case was thrown out of court after it emerged a detective had not handed over text messages from the accuser's phone.
The CPS launched a review of every live rape and serious sexual assault prosecution in England and Wales and, along with police, implemented a plan to try to fix failings in the system.
Some 93,000 officers have undertaken training, while police hope artificial intelligence technology can help trawl through the massive amounts of data stored on phones and other devices.
In rape and sexual assault cases, prosecutors also now use disclosure protocols previously used in terror trials.
The digital consent forms can be used for complainants in any criminal investigations but are most likely to be used in rape and sexual assault cases, where complainants often know the suspect.
The Centre for Women's Justice (CWJ) said a legal challenge is expected from at least two individual women who have been told by police their cases are likely to collapse if they do not cooperate with requests for their personal data.
The law firm said the new measures were "clearly having a deterrent effect on the reporting of rape allegations", giving the example of a woman, referred to as "Olivia", who recently reported rape to police.
She said: "The data on my phone stretches back seven years and the police want to download it and keep it on file for a century.
"My phone documents many of the most personal moments in my life and the thought of strangers combing through it, to try to use it against me, makes me feel like I'm being violated once again."
Police and prosecutors have tried to reassure victims of crime that only material relevant to a potential prosecution will be harvested, but the forms state even information of a separate criminal offence "may be retained and investigated".
The Information Commissioner's Office said it has launched an investigation into use of data extraction technology on the mobile phones of suspects, victims and witnesses.
A spokeswoman said: "We are also currently looking at concerns raised around the collection, secure handling and the use of serious sexual crime victims' personal information."