That is according to new figures from Revenue which show that the Cork-based firm has received fees from Revenue totalling €8.23m since March of 2013.
Abtran started with six people in 1997 and now employs 1,100. In 2013, it expanded after securing the contract with Irish Water to operate its call centre.
The figures for the last quarter of 2014 just released by Revenue show Abtran received €1.265m.
However, general secretary of the Civil and Public Services Union, Eoin Ronayne yesterday described the payout by Revenue as “dead money” and called on Revenue to appoint full-time staff to do the work in-house after the contract with Abtran expires.
The union represents 2,400 employees at Revenue and Mr Ronayne claimed that the €4.65m last year would be sufficient to employ 150 full time clerical officers to carry out the work.
He said: “We were always opposed to outsourcing the work. Revenue has told us the reason it put the work out to tender was that there was a recruitment embargo in place.
“Now that the embargo has been removed, we believe that there is no longer an excuse not to have the work done in-house.
A Revenue spokeswoman said: “Revenue is satisfied that the external service provider has assisted Revenue in the provision of a flexible, scalable response to unpredictable and variable demand for services.
“A key aspect of the service is the provider’s capacity to quickly scale operations up or down in response to call volumes.”