(12:30 p.m. GMT) -- P&O Cruises has emailed passengers telling them the daily service charge will rise from £6 to £7 per adult, per day, on all cruises from 23 March 2018.
The line states: "We have recently made a small change to our Service Reward Programme.
"We know that rewarding really good service as it happens just isn't convenient, so our Service Reward Programme provides a simple one-off way for you to say thank you for all the service you receive.
"For cruises departing 23rd March 2018 onward, this amount changes for each guest (over 12 years of age) to £7 per day."
It is the second time in a year that the tip amount has increased. The line raised charges from £5 to £6 on 27 March last year. Previous to that, P&O Cruises raised its Service Reward Programme charge in May 2015, increasing the daily fee from £3.95 to £5.
Cruise Critic members have reacted with dismay on the message boards.
Josy1953 said: "While this is not a deal breaker, I do think that P&O really do need to sort out this gratuity situation so that everyone pays -- not just those of us with a conscience."
Pidgeofcdf said: "For the staff it won't be a 16% increase. That £7 has to be shared between 3, 4 or more people. Not forgetting that if somebody marks the cabin steward less than excellent, he might not get his share. System definitely needs addressing, but sadly [it] seems P&O aren't listening."
While Davecttr said: "P&O Australia include tips in the fare, so it is technically possible to do it here. They should implement it as soon as possible and put an end to all the arguments."
--By Adam Coulter, Managing Editor, U.K.