ARMS shares were down by almost 33 percent as of 0949 GMT (0449 ET).

Top investor Samin Tan, an Indonesian businessman, last month requested a general meeting seeking to appoint directors to the board who support him as he tries to regain control of the struggling coal miner.

ARMS said in a statement that Tan had not explained why he seeks to change the board.

The company said such a move would add uncertainty to a $450 million refinancing of bonds maturing in July which is vital for the firm.

"The failure of that process would lead to default on the (notes) and possible suspension of trading in ARMS shares and the loss of ARMS's premium listing," it said.

Such changes would also create a risk that the company's main holding, the Berau coal asset in Indonesia, would be operated in the interest of Tan and his company Borneo rather than in the interest of all shareholders, it said.

Tan, who became the largest investor in the company following a restructuring last year, is battling debt issues and one of its creditors, Austrian bank Raiffeisen, took over roughly half of his voting rights in November.

ARMS, hit by internal battles and a tumble in coal prices, has seen its shares lose as much as 99 percent of their value since its London listing in 2010. They rose on Dec. 31 after a court ruling in its favor ordering a former executive to repay $173 million.

(Reporting by Silvia Antonioli; editing by Jason Neely)