The European Commission is calling for action, claiming charges on Channel Tunnel crossings are too high.
According to the competition watchdog, both passengers and freight services are paying too much for the tunnel link.
It says the high prices charged to the train companies get passed on to customers, which then puts people off and forces them to use roads, causing congestion and pollution.
It claims that as a result, 43% of the Channel Tunnel’s capacity is currently unused.
European Commission vice-president Siim Kallas said: "’The Channel Tunnel is not being used to its full capacity because of these excessive charges.
"As a result, more freight is being carried on lorries instead of by rail, freight operators and their customers are being over-charged, and passenger are paying over the odds for their tickets. The current regime is also stifling growth in the rail sector."
The commission has called on the British and French governments to look into the pricing structure.
In its defence, Eurotunnel said it "has always sought the development of cross-Channel traffic and concentrates significant resources on this goal".
"Access charges are defined in the Railway Usage Contract (RUC), signed in 1987 by the
operators, BRB and SNCF," it said.
It said it "regrets that some major railway operators have had such difficulties in their
domestic markets that they have abandoned cross-Channel traffic, leading to the visible
reduction in volumes" and said that to its knowledge, only Eurostar is contesting a claimed lack of transparency in 2014 access charges "finding issue with a contract which it has applied for 19 years".
