Stony Mountain Institution, a medium-security prison north of Winnipeg, is under a full lockdown as a search continues for contraband.

Leah Grove, an assistant warden, confirmed that guards are looking for contraband but would not specify what they are exactly searching for.

Grove said the prison went into lockdown Thursday at around 1 p.m. CT.

No visitors were allowed at the prison on Friday and inmates were not permitted to leave their cells while the search was underway.

According to information obtained by CBC News, the search was being done because the institution received two tips suggesting a firearm had been smuggled inside.

Union officials told CBC News that they are not pleased with how the information about the tips was handled.

The union said some guards were directed to do pat downs without knowing of the possibility that a firearm may be involved.

The guards who were told to do the searches do not wear bullet-proof vests and not all are trained to deal with firearms.

The union said it has contacted officials with the federal labour department and were told the risk was too great for traditional pat downs.

While the information has not been confirmed, the union believes a gun may have been thrown over a prison fence.