Europe will consider this week whether to follow the United States by bringing in tighter controls on "conflict minerals" from war zones, but critics say the measures risk being watered down.
Armed groups in areas such as the Democratic Republic of Congo often fund their activities through the sale of precious metals and those used in electronic goods such as laptops and mobile phones.
The European Parliament will vote on a resolution this week that would force the EU's smelters and refiners to use responsibly sourced minerals, while encouraging other businesses to self-certify their supply chains.
The aim is to ensure profits from the key "blood metals" -- tungsten, tin, tantalum and gold -- do not go to warlords.
It is inspired by the Dodd-Frank Act, a 2010 US financial reform law under which US companies must inform regulators if they use metals from DR Congo or neighbouring countries.
But the conflict minerals have themselves sparked a battle in Strasbourg, the French city that is home to the European Parliament.
Leftist MPs and rights groups want the regulation to be compulsory across the board, not just for the 20 smelters and refineries in the bloc that would be affected, and are trying to pass amendments to the resolution.
"This is now or never for us. It will be decisive," Maria Arena, conflict minerals spokeswoman for the Socialists and Democrats alliance in the parliament, told AFP.
"We want to have a mandatory system for all of the supply chain."
But they face stiff opposition from right-wing lawmakers and pro-business lobbyists, who are backing the resolution as it is and favour a more voluntary approach to the regulation of conflict minerals.
"The voluntary approach will interest the avant-garde of responsible companies to participate," said Romanian EPP member Iuliu Winkler, who is steering the legislation through parliament.
- Star campaigner Mukwege -
Leading the charge for compulsory regulation is Denis Mukwege, a surgeon in the Democratic Republic of Congo who last year won Europe's top rights prize for his work treating victims of mass rape.
"We want the measures to go further," Mukwege last week told the European Parliament, the same venue where he was presented with the Sakharov human rights prize in November.
The campaign is also backed by Edward Zwick, the Hollywood producer of the hit Leonardo DiCaprio film "Blood Diamond" about how the gemstones financed the 1990s war in Sierra Leone.
Amnesty International, the London-based rights group, said all companies should have to show their supply chains were safe.
"We want companies to identify the smelters and refiners they are sourcing from and whether they have put measures in place to identify and mitigate the risk that the trade of gold, tantalum, tin and tungsten is fuelling conflict," Nele Meyer of Amnesty told AFP.
Compulsory regulation would also mean that Chinese and other non-EU firms that want to export goods to Europe would be under pressure to check the sources of minerals, said campaign group Global Witness.
But supporters of the European Parliament resolution being voted on this week say it is in fact stronger than the original proposal by the European Commission -- the executive arm of the 28-nation bloc -- which would have made all regulation voluntary, including for smelters.
Lobby group Business Europe said the voluntary approach encouraged companies to "develop responsible management schemes".
Tech giants like Apple and Hewlett Packard have previously made efforts to ensure the traceability of their supplies.
There have also been criticisms of the Dodd-Frank act for having unintended side effects, such as causing businesses to pull out of DR Congo altogether, leaving thousands of miners out of work and vulnerable to recruitment by armed groups.
After this week's conflict minerals vote, EU countries will have further talks on the issue before working out a compromise with the European Commission, sources close to the matter said.