The Steam Packet says the company has absorbed much of the aditional costs of global fuel price rises over the last few years.
Since the Spring, they say that's involved several million pounds.
The firm has announced a rise in the freight fuel surcharge to £8 per metre. The passenger surcharge doubles to £5 per single journey.
The rise has met with dismay in the Manx carrier sector.
But Director of Harbours, Captain Mike Brew, says the company is not charging its full entitlement under the standing agreement with the Department. That was signed between the Packet and the Department three years ago, permitting rises that reflect the spiralling global fuel price.
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