If it's a PRSA, the limit for tax relief is based on the employee's age, e.g. for an employee in their 30s contributions by employee and employer should not exceed 20% of income in a tax year. Any excess will be treated as BIK.
If it's an Occupational Pension Scheme, the contribution limits by an employer are based on the employee not over-funding, i.e. providing with a pension at retirement in excess of Revenue limites. There are limits but they're more generous than those applying to PRSAs.