TESCO is investigating allegations of major fraud at one of its Irish stores, the Herald has learned.
The alleged fraud is believed to involve the loss of tens of thousands of euro arising from activities at the supermarket.
The matter is being dealt with internally.
The probe involves the supermarket chain's branch at Edenderry, Co Offaly.
It is understood store officials travelled from Britain to take part in the inquiry into the alleged fraud.
A spokesman for the company said Tesco policy was that it did not comment on "matters of an internal nature".
A Siptu spokesman also said he was not in a position to comment on the investigation.
According to sources, the alleged fraud was discovered by security staff at the supermarket who then reported it to their superiors.
It is not known if anyone has been suspended from work in connection with the investigation or if the matter will be referred on to the gardai.
Around 110 people are employed at the Edenderry store, which nearly doubled its workforce with its recent expansion.
Tesco Ireland is the largest retailer in the State with 116 stores as well as 15 petrol stations. It employs 13,500 people.
Last year, the company reported a 5.2pc increase in Irish sales revenues to €3.15bn for the 12 months up to the end of February 2009.
Over that period the retailer opened 16 new stores.
Because of this expansion, like-for-like sales were down 4.2 pc over the period "reflecting the significant slowdown in economic activity and consumer spending during the final quarter of the year", the company said in a statement at the time.
Figures have not yet been released for this year.
Tesco has said previously that the economic situation is "challenging" and that it has been cutting prices to reflect falling demand.
In statements issued, the company said a combination of tight cost control and more international buying meant its Irish operations had reported a solid performance despite trading conditions worsening.