The suit was filed by two Elliott vehicles against the LME and its clearing house in the English High Court on June 1, according to a statement issued by Hong Kong Exchanges & Clearing Ltd., the parent company of the defendants. “The LME management is of the view that the claim is without merit and the LME will contest it vigorously,” it said in the statement.

The move by the activist investor ratchets up pressure against the LME, which has been widely criticized for its decision to halt trading and cancel bets. The LME is also facing a review by UK regulators after it undid billions of dollars of transactions and halted trading for over a week. The nickel market has been stuck in an extended limbo of low liquidity and volatility since the crisis.

Elliott’s lawsuit is challenging the decision to cancel trades, claiming it was “unlawful on public law grounds and/or constituted a violation of their human rights,” according to the statement. The statement didn’t elaborate what trades Elliott had executed or the impact of the cancellation. The claimants were Elliott Associates, LP and Elliott International, LP.

The activist firm is renowned for driving a hard-line, most famously leading a 15-year standoff against Argentina over a debt default.

Elliott couldn’t immediately be reached for a comment. 

As nickel prices spiked in March, the exchange issued more than $7 billion of margin calls — nearly four times the previous daily record. It has said it acted in the interest of the market as a whole when it halted trading. Goldman Sachs Group Inc. is among those that have criticized the exchange, while Tower Research Capital, one of Wall Street’s oldest electronic market-makers, reined in its trading activity on the LME and put its exchange membership under review.

Those at the center of the historic squeeze, nickel tycoon Xiang Guangda and his Tsingshan Holding Group Co., have since reduced the total bet by more than half. The move is seen as lowering cash flow stress on the world’s biggest nickel producer, easing pressure on its banks and removing a key overhang for the LME and its nickel market.

Nickel, which is used to produce stainless steel and in rechargeable batteries, spiked in March before the LME’s decision to suspend and cancel trades. The market reopened with new daily price limits in place after Xiang reached the standstill deal with his banks, but volumes remained well below normal levels even three months later.

The spillover effect of the crisis might have a profound influence on the market. Bloomberg reported previously that JPMorgan Chase & Co., the biggest in metals by far, was reviewing its business with some commodity clients, a move that threatens to drain more liquidity out of the sector. The LME has repeatedly defended its decision. The cancellations were made “retrospectively to take the market back to the last point in time at which the LME could be confident that the market was operating in an orderly manner,” it said in Monday’s statement.

The suit will also add pressure on the Hong Kong exchange, which is already suffering under a drought of initial public offerings. Back in 2013 and 2014 the firm was hit by U.S. litigation over anti-competitive and monopolistic behavior in connection with aluminum metal warehousing. The cases were dismissed but ended up costing the bourse in legal fees, hurting its bottom line.