An inquiry is underway at Barlinnie after a car was firebombed outside a prison officer's home.
It's believed the guard involved has been suspended amid concerns that contraband may have been smuggled into the jail.
The Scottish Prison Service investigation is understood to follow an incident at HMP Barlinnie earlier this month.
And the Daily Record reports, comes after the officer's car was targeted by criminals in May.
The latest development follows an arson attack in the staff car park at the prison in January, when inmates were heard cheering as two motors were set on fire.
A source told the Daily Record: "It's not actually clear what this officer was taking in, but there's a lot going on at Barlinnie now, with gangsters attempting to coerce officers to take stuff in, mainly phones and drugs.
"It starts out as a bribe made and officers can get approached away from the jail.
"But as soon as anyone shows weakness and takes even the smallest package in, that's it. They've effectively sold themselves.
"There isn't any way of putting in your notice and resigning from the gangland postal service because they have a hold over you with blackmail and, by this time, they know where you live and who your family members are."
The source added: "There's been a few officers' cars targeted in separate incidents and it's difficult not to consider that they're linked."
At the firebombing incident in January, a white car and a red vehicle were engulfed in flames.
The melted cars were removed from the scene by a recovery vehicle just hours later.
Both of the motors were completely gutted by the flames, with the white car's front wing melting away under the intense heat.
Officers cordoned off the car park.
Footage showed multiple cars on fire as thick smoke billowed across the car park.
A Scottish Prison Service spokesperson confirmed that a member of staff had been suspended but refused to give further details.
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