Mining giant BHP Billiton is facing a $5bn (£3.8bn) claim for damages over a dam collapse in Brazil in 2015.
Law firm SPG, which is representing than 200,000 Brazilian claimants, said the company "knew of the risks" at the Samarco mine in Minas Gerais state.
The claim, which was served at Liverpool's High Court on Tuesday, is the largest in UK legal history.
BHP, an Anglo-Australian firm listed in London, rejects all of the charges.
Tom Goodhead, partner at SPG, said: "The repeated warnings and recommendations of dam safety experts were acted upon too slowly, or sidestepped entirely.
"Driven by concern for declining revenues amidst the falling market price of iron ore, the company took risks, increased production and turned a blind eye to dangers that ultimately claimed lives and destroyed communities."
The Samarco disaster in Minas Gerais state, south-eastern Brazil, killed 19 people and displaced 700, and is considered the country's worst environmental disaster.
When the dam burst, it unleashed a deluge of thick, red toxic mud that wiped out the village of Bento Rodrigues.
It also polluted the Rio Doce river and Atlantic Ocean 650km away, devastating wildlife and tainting drinking water for hundreds of thousands of people.
The lawsuit is being brought on behalf of 235,000 Brazilian people and organisations, including municipal governments, indigenous tribes, utility companies and the Catholic Church.
It claims BHP failed to act on repeated warnings from independent experts about the dam's integrity.
Instead, it claims the mine continued to increase output of iron ore, leading to heightened water levels.
Mr Goodhead said: "BHP was woefully negligent in its duty of care and the damages sought are entirely commensurate with the devastation the company has wrought upon the people of Minas Gerais, [the state of] Espirito Santo and Brazil."
BHP has rejected all charges against the company, as well as current and former staff.
On Tuesday company spokesman Neil Burrows said the miner intended to defend itself against the claim.
Samarco, the mining company involved in the disaster, is co-owned by BHP and Brazilian firm Vale.
Both firms have faced big fines in Brazil, and have had to pay millions of dollars into compensation and remediation programmes.
BHP has separately settled a class action by US investors over the disaster and continues to battle Australian shareholder lawsuits,