Beginning on April 1, 2017, Norwegian Cruise Line will be increasing their gratuities amounts. Currently for standard cabins guests are asked to pay $13.50 per person, per day. However that amount is being increased to $13.99 and $16.99 for suites. This is with the exception of the Norwegian Sky. Gratuities for the Sky increase to $18.99 per person, per day for standard cabins and $21.99 for suites.
Norwegian automatically adds the gratuities onto guests accounts however they can adjust those amounts if they choose to but only by contacting guest services after returning from their cruise. So the cruise line does not make is especially easy to make adjustments to the gratuities amounts.