Eurostar has defended limiting the amount of alcohol passengers can carry on its trains as necessary to "maintain a pleasant environment".
The train operator explained its position after customers complained on social media about changes to the policy.
It allows one bottle of wine or four cans of beer and no spirits.
Previously, there were restrictions on ski resort routes and temporary ones for sporting events.
Although Eurostar says it made the changes last year, passengers appear to have only just started to notice.
Passenger Claire Tate told the Press Association that the policy was disgusting and she will reconsider using Eurostar in the future.
"I think the policy is there for sports fans who come on drunk and disturb other holidaymakers. Something should be in place - like an extra fee - for those types of travellers".
Mark Smith, a rail expert who runs his passenger seat61.com website which says it promotes train rather than air travel, tweeted that "Eurostar has quietly changed its luggage policy" which was "completely unnecessary".
"Previously its policy was easygoing, it was sort of what you would expect. I'm aghast at the change, it seems draconian," he told the BBC.
Mr Smith said the change would make travelling by train "more stressful" for many passengers.
Eurostar said the change to its alcohol policy was made last autumn.
"This decision was made to maintain a pleasant environment on board for all our travellers. Those that wish to take more with them for consumption at home can do so using our registered luggage service, EuroDespatch," the company said.
Its luggage service, EuroDespatch, charges a minimum fee of £30 per item.
Eurostar would not say how many customers had been stopped at security checks with too much alcohol since the limits were put in place.
Neither did it say whether there were any restrictions on the amount of alcohol that can be bought on its trains.
"All luggage goes through a scanner as it does in the airport and Eurostar reserves the right to confiscate any alcohol over those limits. Alcohol consumption on board is monitored by our team," Eurostar said.
Another passenger complaining about the change was Will Roberts who said: "That's crazy. You mean I can no longer bring a six pack of Belgian beer back home in my bag after trip to Brussels? Is there a way to convince them to change?"