The French interior minister Bernard Cazeneuve has accused Eurotunnel of not doing enough in light of the “worsening situation” in Calais.
It comes after a migrant died in the latest incursion on the Channel Tunnel, as Eurotunnel reveals it has blocked more than 37,000 people attempting to cross into the UK this year.
The letter from Mr Cazeneuve to Eurotunnel president Jacques Gounon is dated July 23 and was leaked to the French press.
It said: “In my analysis, the Eurotunnel group, which has jurisdiction of the security, hasn’t made enough effort in light and proportion to the worsening situation.
“I would like you to have a further look at the human resources you are planning on dedicating to securing the site”, he added, believing the company has cut its security staff by two-thirds since 2002.
He said: “In the same time frame, the state has multiplied its resources by five, and...350 members of the state security police force (CRS) and police officers work together every day to prevent intrusions.”
Eurotunnel has said it has gone “beyond its contractual obligations” to protect the terminal in Coquelles, near Calais.
The migrant's death comes as some 1,500 people were successful in breaching the fences at Calais last night, and 2,000 stormed the French terminal the night before.
Eurotunnel revealed the scale of the problem as it came under increased pressure to do more to deal with the crisis.
A spokesman for Groupe Eurotunnel, which manages and operates the Channel Tunnel, said that since the arrival of migrants in the area around Calais, it has invested more than €160m, including €13m in the first six months of 2015, in physical resources - fences, cameras, infra-red detectors – and personnel.
He added: “These considerable investments have already been followed in the second half of the year with new fencing around the platforms. Security patrol staff has been doubled to reach 200 employees, including sniffer dog patrols.
“To support the efforts of law enforcement in the Calais area, Eurotunnel has also provided buses to the authorities to enable them to remove any migrants intercepted.”
The spokesman also said that Eurotunnel has kept the Intergovernmental Commission for the Channel Tunnel and authorities informed, over several months, about the “explosion” in the number of migrants present in Calais.
“Since 1 January 2015, Eurotunnel has, using its own resources, discretely intercepted more than 37,000 migrants, who have been handed over to the law enforcement authorities, and has registered thousands of complaints, all of which have been filed with no further action by the procureur (legal official) of the court in Boulogne.
“The continuous pressure exerted every night is above and beyond that which a concessionaire can reasonably handle and requires a constructive and appropriate response from the governments.
“In this context, Eurotunnel and its employees, who hold to their task despite the psychological pressure that weighs on them, continue to guarantee a rapid and safe Channel crossing for its millions of customers.”
The Road Haulage Association has called on France to deploy its military to secure the port of Calais, saying that the police can no longer cope.
While businesses of all sizes in Kent have united to call for the issue to be dealt with quickly, as they struggle to receive supplies and welcome visitors
Some firms in the area are also reporting huge falls in customers as Operation Stack causes queues of traffic to form outside their businesses.