Steelmaker Arcelor has made a 3bn euro (£2.1bn; $3.6bn) hostile bid for Canada's Dofasco after talks between the firms broke down.
The Luxembourg-based firm said it had approached Dofasco investors with the 40-euros-a-share bid after the two had been unable to agree on a deal.
Arcelor said it had first approached Dofasco - Canada's largest steelmaker - at the start of the year about a possible deal, but was unable to reach agreement.
As a result, it had decided to approach Dofasco shareholders directly with what it described as a "compelling offer".
"For Dofasco, the question is not if it should join forces with another industry player but when and with whom," said Guy Dolle, Arcelor's chief executive officer.
"We strongly believe that Arcelor is the best partner for Dofasco and that this is the right time."
Dofasco is a leading supplier to the car, construction, energy, manufacturing and packaging industries - with operations in Canada, the United States and Mexico.
Arcelor is a leading player in Europe and Latin America and has been looking to expand in the US and developing markets such as Africa.