Channel Tunnel operators could launch a legal complaint under anti-competition laws if the Newhaven-to-Dieppe ferry line continues to be subsidised.
The Transmanche ferry route is currently run by DFDS Seaways but its contract expires next year.
With no new operator yet to come forward, Eurotunnel, which runs the rail link between Kent and France, said it would complain to Brussels bureaucrats if the Newhaven link continues to be significantly propped up by public funds.
It comes as local authority leaders in Sussex are still looking at ways to keep alive the line, which is currently subsidised by the French government, and to save about 500 UK jobs.
A spokesman for Eurotunnel confirmed that the firm had launched a legal complaint previously about the Newhaven route, which is believed to have cost French taxpayers £190 million over the last ten years.
He added: “As far as I’m aware, the contract is still open to tender.
“But if there’s a significant subsidy then we would maintain the same position that if a service is subsidised by local authorities it’s an unfair position of competition against those privately-owned or market-constrained firms.”
The General Council of Seine-Maritime (CGSM), which subsidises the link, is looking for new investors.
When the announcement was made, Nicolas Rouly, president of the CGSM, said: “I wonder about the relevance of a link that depends solely on public funds.This is a potentially difficult decision to take to stop the line. But we have spent £190 million of public money in ten years.”
Speaking at a meeting of the Greater Brighton Economic Board last week, Rob Blackman, leader of Lewes District Council, said: “The French are in a bit of flux at the moment, still insisting that we part-fund the ferry.
“East Sussex [County Council] is unclear and are going to review it.
“The Channel Tunnel lodged a complaint under anti-competitive practices so it’s quite unlikely we’re able to support a ferry itself.”