Fortescue Metals is planning to appeal a ruling by the Australian Competition Tribunal not to force BHP Billiton and Rio Tinto to open up their two main railroads to Port Hedland - Mount Newman and Hamersley to other miners.

In a statement, FMG said it is likely to request for a retrial to the Federal Court after reviewing the national competition tribunal's decision on BHP's Mount Newman and Rio's Hamersley railways.

Last night, the Competition Tribunal disclosed that the expenses in letting smaller mining companies use the Mount Newman and Hamersley lines ''were so great that access would be contrary to the public interest.''

Fortescue, however, did succeed in convincing the tribunal to open up BHP's Goldsworthy line to other miners. This was a significant victory according to the FMG executive director Russell Scrimshaw.

"The Tribunal has upheld Treasurer Wayne Swan's declaration that there is spare capacity on the railway lines, which can be utilised to maximise the economic benefits to Australia from increased iron ore exports," Mr Scrimshaw said.

"An excellent outcome for Australia."

Fortescue shares plunged eight cents, or 1.94 per cent, to $4.04 in recent trade.