Opposition is growing from steelmakers across the world against miner BHP Billiton's £75bn hostile takeover plans for its rival Rio Tinto.
Companies, particularly in China, Japan and Europe, say a combination of the two would simply be too powerful.
It would become the third biggest group in the world, dwarfed only by Exxon Mobil and General Electric.
BHP accounts for around 15% of global iron ore supplies, while Rio Tinto is responsible for another 24%.
That would give them almost 40% of global supplies and thus a virtual stranglehold on prices, it is feared.
BHP has offered 3.4 of its shares for each Rio share, after offering three shares some weeks ago.
Rio had rejected the earlier bid as being too low - and has also snubbed the latest one as seriously undervaluing it.
There is now speculation that a rival suitor will step in, possibly from China.
Shares in both BHP and Rio fell in the wake of BHP's offer and Rio's rejection of it.
The approach had come only hours before a deadline from UK regulators for BHP to "put up or shut up" - in other words to make a concrete proposal or hold off for at least six months.
It's impossible to overestimate how seriously the steelmakers of the world are taking this issue. At a time of rising energy and oil costs, the potential for high further increases in ore costs is a very worrying prospect. I am sure this story will dominate the steel world for some time.