European competition regulators are investigating a deal to share production between the world's second and third-biggest producers of iron ore, Rio Tinto and BHP Billiton.
Concerns in Brussels over a 2008 merger plan abandoned by BHP Billiton late that year have now switched to a modified agreement signed on December 5 last year.
The deal was to share iron ore assets in Western Australia, 'leaving the marketing activities of the companies separate'.
The European Commission said it would focus on the effects of the proposed joint venture on the worldwide market for iron ore transported by sea.
Iron ore is central to the manufacture of steel, on which the car and construction industries - as well as many consumer goods - are based.
The EU insists that the decision to investigate 'does not imply conclusive evidence of an infringement', but stressed that there was no binding deadline for the probe's outcome.
BHP Billiton last week posted record iron ore production figures for the second half of 2009, amid rising commodity prices driven largely by Chinese demand. Also this month, Rio Tinto beat annual forecasts with a record-breaking fourth-quarter of iron ore production.
