Shareholders unhappy with the plunge in the value of shares in Altice plan to sue the French and US telecoms firm, which said Wednesday it is the victim of a malicious PR attack.

A lawyer specialising in cases against large companies, Frederik-Karel Canoy, said the lawsuit to be filed in France would accuse Altice of misleading investors.

He said the plaintiffs estimate that the firm had understated and falsely claimed it had complete control over its debt.

Altice spokesman Arthur Dreyfuss told AFP that as a listed company it regularly reports financial information and is under the supervision of regulators.

"We call for the utmost prudence concerning what appears to be a manipulation, a malicious public relations manoeuvre and attempt to destabilise the firm via the media," he said.

Shares in the Amsterdam-listed firm have fallen by around half since the firm released its latest results at the beginning of the month.