The Channel Tunnel operator is threatening to sue the British government for as much as £200m (around €282m) if ministers decide to shut down overnight services amid the migrant crisis.
Eurotunnel says closing the service at night would result in significant losses and accused British ministers of "sowing panic among customers and investors", according to The Daily Telegraph and The Times.
Company president Jacques Gounon reportedly wrote a letter to Christopher Irwin, the head of the UK delegation to the Channel Tunnel Intergovernmental Commission, threatening to seek compensation.
"Under the concession agreement Eurotunnel would be obliged to claim for losses which we estimate could easily attain the level of circa £200m per year," the letter reportedly said.
"Any significant reduction in overnight services through the Channel Tunnel would have a grave impact not only on the concession holder but also on the UK economy.
"We believe it would be far better for resources to be focused on resolving the 'Calais crisis' rather than sowing panic amongst customers and investors and, ultimately, damaging the economy."
Thousands of migrants have attempted to sneak over the fence along the train tracks at Calais leading to the tunnel and ultimately to Britain.
At least nine people have died, and a Sudanese man walked almost the entire length of the Channel Tunnel - around 50km - before being arrested.
In the most recent case of breached security, a group of 30 migrants walked inside a security zone at the Coquelles Channel Tunnel terminal after guessing the security code, the Telegraph said.
They were apparently able to guess the code by examining which numbers were dirtiest or most worn on the keypad.
The UK government has promised to boost security in Calais by sending additional security guards, sniffer dogs, fences and surveillance equipment including more CCTV to tackle the crisis.
It is also reportedly considering a closure of the tunnel at night.
In the UK, hauliers have also condemned any possible night closure of the tunnel, according to the Financial Times.
Donald Armour, of the Freight Transport Association, told the newspaper: "I think if this was to go ahead it just shows again that the government is not thinking about the freight side of the business.
"They are just concerned about UK security."
