Legal letters being sent to prisons are being photocopied by wardens amid fears they are soaked in drugs.
In the latest method of smuggling drugs into prison, inmates are getting accomplices on the outside to spray their post with drugs.
Prison officers are now being forced to open mail and photocopy the contents to crackdown on the new fad.
A report by inspectors from the Independent Monitoring Board (IMB) revealed that fake legal letters are being sprayed with Spice, a former legal high.
The drug dissolves into the paper and then smoked as joints.
The IMB report into HMP Wealstun, a category C prison in West Yorkshire holding just over 800 men, stated that prison healthcare staff were called out up to 10 times a day to inmates suffering the effects of psychoactive substances, such a Spice.
It stated: "PS (psychoactive substances) continues to be a major problem in the prison, increasing the level of violence on the wings and resulting in the hospitalisation of prisoners and officers.
"Much of the PS comes over the wall; this is a difficult problem to resolve owing to the length of the perimeter.
"Where there is suspicion that incoming letters have been soaked in drugs, they are photocopied.
"This has resulted in an increase in complaints from prisoners, as bogus legal mail is a significant problem and legal mail should not be opened."
The report added: "There are 8-10 calls per day but staff are becoming more adept at dealing with these calls.
"Staff are well trained on PS drugs, often spending more time with the patient which can have a knock-on effect of some clinics being canceled.
"However, this reduces the need to call an ambulance."
The report states that the drug is also responsible for an increase in violence.
"There has been a considerable increase in assaults on prisoners and staff over the year compared to the last reporting year, which the Board feels is caused by the increase in drug use and the frustration prisoners feel when regimes are curtailed due to lack of staff," it adds.
"The main reasons for assaults are arguments, issues with staff, retaliation and debt.
"Psychoactive Substances (PS) continue to be a major issue for healthcare within HMP Wealstun."
Last week Public Health England warned that double the number of people are coming out of prison testing positive for Spice as are going in.
Dr George Ryan, of Public Health England, said the drug, which is notorious for turning entire high streets into “zombie zones”, is “very affordable” for prisoners.
Data compiled by PHE from prisoners in the North West indicate that 16 per cent test positive after finishing their sentence, compared to eight per cent at the start.
“Currently it is the adult male prisons which face major problems due to Spice,” Said Dr Ryan.
“It tends to be more potent than high potency cannabis.
“You have the toxic combination of wide effects, high, variable and unpredictable potency. In a closed environment like a prison it’s particularly challenging.”