British fishing boats will spend 10 days a fortnight docked in harbours under a "disastrous" deal hammered out in Europe, Labour has said.
Crews will be confined to ports because of a cut in the number of days they are allowed to fish, MPs were told.
The Government insisted the restriction, designed to protect cod stocks, was the best long-term outcome for the UK fleet.
But shadow fisheries minister Fiona O'Donnell claimed: "This deal will mean a cut of between 15% and 25% in the number of days white fishing vessels can put out to sea in 2012.
"Fewer days at sea could lead to the unintended consequence of more damage to fish stocks and higher levels of discards as fleets rush to catch all they can in their allotted time."
She accused fisheries minister Richard Benyon of "abandoning" his negotiating red lines before signing the agreement and said fishing experts and conservation groups "described this deal as a disaster".
Updating the Commons on talks with European fishing ministers on the Agriculture and Fisheries Council, Mr Benyon said he managed to avoid "dire consequences for significant elements of the UK fleet".