Could Bonus be reduced for those who took maternity leave

An annual bonus scheme which is made up of a profit share and a performance element is being considered.

Could those who took maternity leave within the year receive reduced payments with the calculations taking into account the period that they were not at work? (excluding the 2 week compulsory maternity leave)

Would other absences (eg sick leave, sabbaticals etc) have to be taken into account as well?