Bluebridge cancelled six services between Picton and Wellington on Tuesday; the 2am, 8.15am and 1.30pm sailings from Wellington and the 2.30am, 7.45am, and 7.15pm sailings from Picton.
Affected customers were being contacted by the ferry service for alternate sailing options.
Bluebridge's website said "storm-force southerly winds and large swells" were forecast for Cook Strait from late Monday 30 December and throughout most of New Year's Eve.
Interislander cancelled two morning sailings of Aratere - the 6.15am from Wellington and the 11am return from Picton.
All passengers had been shifted to other sailings and the swells were due to slowly ease from this afternoon, it said online.
Anyone who was worried about seasickness should sit at the back of the ship and should not sail on an empty stomach, it said.
