The Union alleged that the FDNY violated NYCCBL § 12-306(a)(1) and (4) by failing to negotiate over a new requirement that employees who volunteer for overtime must work the shift, find a replacement, or lose their ability to exchange shifts for 90 days. The Union also alleged that the FDNY failed to negotiate over a change in employees’ ability to exchange shifts if they call in sick for an overtime shift. The City argued that the new requirement was intended to reduce understaffing caused by employees using sick leave on days they were scheduled to work overtime, that its actions are within its discretion, and therefore the new requirement is not a mandatory subject of bargaining. The Board found that the portion of the undisputed change relating to the distribution of overtime is a mandatory subject of bargaining but the portion relating to the City’s decision to suspend mutuals is not. Accordingly, the petition was granted in part and denied in part.