Is it an occupational pension or a PRSA?
My understanding is that with the latter the employer and employee contributions are summed for the purposes of the age related pension tax relief limits.
E.g. if your employer contributes 5% then you can only contribute 25% to reach the 30% limit.
Whereas with an occupational scheme you can contribute 30% even if the employer is contributing another 5%.
This page details bik on pension contributions made by employers