By Leonard Doyle

Published: 11 July 2007

The bus carrying 50 tired and grimy miners had just left La Loma mine when gunmen forced it to stop and dragged two union leaders off. One was shot dead on the spot, the gunmen pumping four bullets into his head. The other was tortured and then killed. Six months later another union leader who had come to the mine was also assassinated.

The men, members of the Sintramienergetica union, had been trying to improve the appalling and unsafe working conditions at a United States-owned mine, which sends huge amounts of coal from Colombia to Europe and North America.

Six years later, a federal court in Birmingham, Alabama, is trying the privately owned coal company, Drummond, for war crimes. This week it heard evidence that the company ordered those killings in March 2001.

It was alleged that a union treasurer, Jimmy Rubio, saw a Drummond official pay a paramilitary leader to carry out the murders. Mr Rubio has been in hiding since his father-in-law was murdered just before he was to give a deposition in the case. The outcome of the trial could have huge implications for several dozen American multinationals being sued under a formerly obscure law, the alien tort claims Act, which was once used to combat piracy.

The 214-year-old law has been used by human rights groups to attack some of the best-known names in corporate America: Exxon Mobil, Chevron Texaco, Del Monte, Citigroup and Bank of America. Five companies, including a Coca-Cola bottler, have been accused by the same trade union of hiring paramilitary groups to kill union leaders.

Chiquita, the banana company, recently admitted paying right-wing militias to protect its Colombia operations. It was fined $25m (£12.5m) this year for giving $1.7m to the militias from 1997-2004. Chiquita said the regular monthly payments by its wholly owned subsidiary Banadex were "to protect the lives of its employees". Such practices were widespread among multinationals in Colombia. The allegation against Drummond is that it used paramilitary violence to keep wages down.

"They thought they could get away with anything, literally get away with murder," said the union's lawyer, Daniel Kovalik. The Bush administration has tried to block the lawsuits, saying they interfere with foreign policy.

The Washington-based International Labour Rights Fund has filed many of the 26 lawsuits. It faces the hurdle of proving links between company policy and human rights abuses. Terry Collingsworth, director of the rights fund, said the purpose of the suits was not to win damages, but to change business practices.

For Colombia, the murders of the three Drummond organisers – Valmore Locarno and his deputy, Victor Orcasita, as well as his successor, Gustavo Soler, who was murdered six months later – were routine. Nearly 90 per cent of trade union leaders killed worldwide die there. Few of the murders are ever resolved. At least 800 union organisers have been killed since 2001. Many have simply fled the country.

Lawyers for families of the three men say the killers "were acting as employees or agents" of the company and have charged it with war crimes in a civil court action under the alien tort legislation, which allows foreigners to file civil lawsuits against US corporations for their conduct overseas.

The families say the war crimes claim is valid because armed groups have been killing each other for decades in Colombia's civil war and that by paying off paramilitaries Drummond had itself committed criminal human rights violations. The lawsuit alleges that Drummond intimidated union activists by allowing "known paramilitaries to freely enter their mining facilities" and permitted pamphlets to be handed out accusing union members of being part of a "guerrilla union".

Drummond, one of the largest coal-mining companies in the world, denies any involvement with the paramilitaries. For decades, landowners and businesses have used private militias to protect them from the guerrillas. And Drummond says the court must first prove that the workers were not associated with these guerrillas. The company, which opened its 25,000-acre Pribbenow mine in 1995, produces about 25 million tons a year, and earns about $2bn a year. Left-wing rebels have bombed the trains that take coal to the coast at least 40 times. And Drummond also pays the government to station several hundred soldiers at the mine.

The union's leaders say they still fear for their lives, and now have the support of the miners' union in Alabama, where 2,000 miners have been sacked since the Eighties when Drummond began investing in Colombia.