In an unexpected move, the European Parliament voted to require all EU importers of four minerals to be certified to ensure they do not fuel conflicts and human rights abuses.
The European Commission had recommended that checks be only voluntary.
Human rights groups praised the vote as a "historic moment".
The decision will now be discussed by member states and the European Commission.
Amnesty International and Global Witness had originally warned that a voluntary system covering European businesses would have watered down the proposals.
Before the vote, the two groups were among more than 150 which signed a letter calling for binding rules that focused on more manufacturers and more materials.
MEPs decided to back a law covering not just European importers that sourced minerals from conflict zones but also companies that used the four materials - tin, tungsten, tantalum and gold - in the manufacturing process.
While an estimated 20 refineries and smelters would be directly affected, the EU also estimates as many as 880,000 firms would have to provide details on the measures they take to avoid the use of minerals from conflict areas such as the Democratic Republic of Congo and the Great Lakes area of East Africa.
Many tech gadgets such as smartphones use conflict materials, so-called because they are mined in warlike conditions and traded by armed groups.
Campaigners had earlier complained that the scheme did not cover minerals and materials such as diamonds, jade and chromite, which are also known to be sources of conflict.

The 22-year-old joined up with his new teammates after the World Cup, but has yet to feature for the Chiefs.
"We have won two games out of three in the Premiership and he's not been here very long," Baxter told BBC Sport.
"He, like a number of other very good players here at Exeter, will have to be patient and when their chance comes they'll have to play very well if they want to stay in the team."
Campagnaro, who has won 18 caps for his country and featured in all four of their games at this year's World Cup, agreed a move to the Chiefs in Janaury from Pro12 side Benetton Treviso.
He has been training with the Premiership club for the past three weeks.
"It's hard for me to say how far away he is, we don't know what injuries are going to happen, we don't know the form of the team, we don't know how our centres are going to play this weekend," added Baxter.
"He could be very close or he could have to be patient for a while, but the A League's not more than two or three weeks away now.
"All the players that haven't played so far will feature in the A League. That will give them an opportunity to play. They may well get an opportunity before then depending on other circumstances."

"Using horse-driven carriages only for joyrides solely for human pleasure is an avoidable activity," the order said.
The court agreed with animal rights groups that the practice was cruel.
Reports say that around 700 families depend on Victoria carriages for their livelihood.
Monday's court order came on a petition filed by animals rights groups which said the horses were often malnourished, denied adequate rest and care.
The Bombay high court in the city of Mumbai ordered that all stables where these horses are kept must be closed down and  directed the authorities to come up with a scheme to rehabilitate those involved in the trade.
Styled on open carriages used during Queen Victoria's times, these horse-drawn carriages have been seen on Mumbai's streets since British times and a ride on them has been one of Mumbai's most-popular tourist attractions for decades.
The drivers of these carriages say that "Victorias are a key part of Mumbai's cultural image" and some of them say they are sceptical about the government's rehabilitation plans.
Usmaan, who is 60, has been working with a horse-drawn carriage since he was 12, says it is going to be difficult for him to adapt to a new job and that he feels like his "hands have been cut off".
The court has also ordered that all horses should be rehabilitated at a care centre.
"The government shall also formulate a rehabilitation scheme for the horses. If any reputed animal welfare organisation comes forward to take care of these horses, then the state government is free to consider the same" the Hindustan Times quotes the court as saying.
Euro MPs have called for companies to carry out mandatory checks to stop "conflict minerals" entering Europe from war zones.
[NEXT_CONCEPT]
Italy centre Michele Campagnaro will have to wait to make his Exeter debut.
[NEXT_CONCEPT]
A court in India has ruled that Mumbai's famous horse-drawn carriages, popularly known as "Victorias", are "illegal" and must go off the city streets in a year.