Paris stock market regulator AMF has issued a rare warning to brokers taking orders for Eurotunnel shares after a sharp rise in the firm's market price.
The watchdog warned such orders were irrevocable and brokers should check clients have enough money to buy stock.
The warning suggests AMF fears the soaring share price may leave some investors unable to pay for shares they buy or deliver shares they have sold.
Eurotunnel shares have almost tripled since resuming trading on Tuesday.
Eurotunnel shares rose 92% in Paris on Tuesday and another 90% on Wednesday.
Thirteen percent of Eurotunnel shares began trading on Tuesday after holders of the other 87% agreed a reorganisation plan for the company, which will cut its debt from �6bn (8.9bn euros) to �2.84bn.
The Anglo-French firm had faced bankruptcy unless its plans were backed by at least 50% of shareholders.
Under the plans the majority of shareholders agreed to exchange their old Eurotunnel shares for the new Groupe Eurotunnel shares, which will not make their stock market debut until next month.