Irish owner ICG is facing a cost hit due to a probable delivery delay for its new ro-pax.
Its Irish Ferries unit told the Irish Times that between 5,000 and 10,000 passengers will be affected by cancelled sailings between 12 and 29 July.
German yard Flensburger had informed the group the EUR 144m ($176m) WB Yeats is "likely to be delayed."
Alternative space is being offered on other ferries, or a full refund, plus a EUR 150 voucher for sailings next summer.
The vessel was contracted in 2016. TradeWinds reported at the time delivery was intended for May 2018.
It will carry 1,885 passengers between Ireland, France and the UK.
Flensburger has been contacted for comment.
