"Poles are not used to travelling by boat and are not always informed about the safety rules that they have to abide to on a ferry. We are asking them to sign these contracts to remind those who are travelling with us just to have fun about these rules," Stena Line's spokesperson in Poland, Agnieszka Zembrzycka, tells Swedish Radio's local channel in Karlskrona in the southeast.
Zembrzycka says that their departures from Poland to Sweden are especially rowdy and that those who breach the contract may be put in the ship's jail cell.
"People should be quiet when they are in their cabins. If you want to party you should go to a nightclub, not to your cabin," Zembrzycka says.
The operator started having live shows and other types of entertainment on these departures two years ago and quickly noticed that it lead to more unruly passengers.
Stena Line's spokesperson in Sweden, Jesper Waltersson, says that they will not ask anyone travelling from Sweden to Poland to sign a similar contract.