Mobile phones are often thrown over prison walls
Prisoners in Scottish jails caught with mobile phones will have their sentences increased in a bid to prevent illegal activity being planned behind bars.
The proposed amendment to existing legislation will also mean jail terms for anyone attempting to smuggle mobiles or SIM cards into prisons.
The Scottish Parliament will be asked to approve the amendment, which would come into force next month.
Prison chiefs also plan to use signal blocking devices in jail grounds.
Currently mobile phones are not defined as "prohibited articles" and are treated as unauthorised property.
Justice chiefs propose amending the prison rules to specifically prohibit personal communication devices, including mobile phones.
From next month, prisoners caught with mobiles or SIM cards, and those who smuggle them in, would be sentenced to 30 days behind bars.
The aim is to clamp down on prisoners who use mobiles to arrange drug deals, intimidate witnesses and organise crime outside jail.
Justice Secretary Kenny MacAskill said: "Serving a prison sentence should not allow the Mr Bigs to continue their life of crime.
"The smuggling of mobile phones into prisons is becoming increasingly difficult to detect as the technology is becoming smaller. But the Scottish Prison Service is committed to searching for them.
"By making possession a punishable offence, we are showing that it will not be tolerated."
He said that, in addition to the proposed amendment to the Prisons (Scotland) Act 1989, a new offence of using a mobile phone in prison with a penalty of up to two years in prison will be contained in the Criminal Justice and Licensing Bill which goes before parliament next year.
Richard Baker, Labour's justice spokesman, said: "Tackling mobile phone use is a vital step in dealing with organised crime being directed from prison. It also might help in stemming the tide of drugs.
"However, our prisons need to be rid of the record levels of overcrowding if this policy has any chance of success.
"For jail security to improve, prison officers need more time to conduct searches rather than just dealing with the day-to-day duties."
A common method of smuggling a mobile phone into jail is through a prisoner concealing it on their body.
Other methods include throwing the device over the prison walls and having them smuggled in by contractors.
In many cases only a SIM card is brought in, allowing prisoners to make calls using shared handsets.