If an employer pays you salary and then you choose to pay some of it as an employee contribution or AVC into a pension scheme, you can claim back the Income Tax but not the PRSI or USC. If the employer reduces the salary and puts the same amount as an employer contribution into a pension scheme, the contribution avoids Income Tax, PRSI and USC and so this would be advantageous for both employer and employee. But Revenue are aware of this - it's known as salary sacrifice and is forbidden. If Revenue notice this, now or in the future, they'll charge PRSI and USC on the contributions as if they were paid as salary.
I'd get the employer to rectify this as soon as possible.
Regards,
Liam
www.FergA.com