Under regulation 15 and regulation 16 of the Working Time Regulations (Northern Ireland) 2016 (“WTR”), a worker is entitled to a period of 5.6 weeks’ paid leave in each leave year (pro-rated for part-time workers). This entitlement equates to 28 days for those who work 5 days a week and is comprised of a minimum of 4 weeks’ annual leave, as well as the domestic right to an additional 1.6 weeks’ annual leave each year, (the latter representing the number of public holidays in the UK). As such, a part-time worker with reduced hours is entitled to 28 days’ holiday reduced pro-rata, which is usually calculated in accordance with the number of days they work each week.

A worker is entitled to be paid in respect of any period of annual leave taken at the rate of a week’s pay in respect of each week of leave (regulation 20, WTR). Holiday pay is therefore calculated with reference to the worker’s pay at the time when the leave is taken, rather than at the time of accrual. If a worker changed from full-time to part-time status after accruing annual leave during their full-time employment, their week’s holiday pay would reflect the part-time salary rather than the full-time salary under the WTR.

However, the WTR do not sit comfortably with the Part-time Workers Directive (97/81/EC) in this regard. This is because the European Court of Justice (“ECJ”) in Zentralbetriebsrat der Landeskrankenhäuser Tirols v Land Tirol [2010] IRLR 631 held that the EC Framework Agreement on part-time work (annexed to the Part-time Workers Directive) precludes a national law under which a worker moving to part-time work "suffers a reduction in the right to paid annual leave he has accumulated but not been able to exercise while working full-time".

In order not to suffer less favourable treatment as a result of moving to part-time work, the worker should, in principle, be able to take the accrued week's leave as if they were still full time.

From a practical perspective, it may be useful to require an employee to take all accrued leave before they move from full-time to reduced hours so that difficulties do not arise in terms of pay and also to help mitigate any exposure to a claim from a worker that they have been treated less favourably due to their part-time worker status.