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.

Altice has grown rapidly since it was founded in Luxembourg in 2001, moving into the cable, content production, telecom, media and online video advertising sectors. 

But the acquisitions, which include France's second-largest mobile firm SFR in 2014 cable operators Suddenlink and Cablevision in 2015, making it the fourth-largest US cable operator were made with debt.

The firm, which posted 23.6 billion euros in sales last year, had debt of 51 billion euros at the end of September.

The latest results shook confidence in investors that Altice would be able to cut costs and increase revenue sufficiently in his French and US acquisitions to make the debt-financing a viable strategy.

Altice has moved quickly to try to shore up that confidence, with the firm's founder, French billionaire Patrick Drahi, retaking the reins.

The firm also announced it would put on hold making any further acquisitions and focus on cutting debt.

Altice shares fell 8.8 percent Wednesday to 7.56 euros, their lowest point since March 2014