Is overtime included in the calculation of vacation and sick leave?

37 This interpretation is reinforced by the parties’ past practice since at least 2005 of not including overtime in the calculation of vacation and sick leave. Additionally, it is well established that a benefit that entails a monetary cost to the employer must be clearly and expressly stipulated in the collective agreement (see Wamboldt v. Canada Revenue Agency, 2013 PSLRB 55 at para. 27). In this case, the union had the burden of proof of showing that on a balance of probabilities, its interpretation should be preferred. It did not convince me that overtime is clearly and expressly included for the purposes of clauses 29.02 and 31.01.