FMG CEO Elizabeth Gaines said the company did not have the capacity to expand its production to take up the excess.
She said the company was running at its nameplate capacity of 165 million tonnes per annum to 170Mtpa and would continue to do so for the foreseeable future.
That is not to mean it is not looking at ways to further optimise its operations.
"We're running our OPFs [ore processing facilities] at capacity," she said.
"But we're always looking to our mine plans to see where we can optimise."
Rio Tinto told the Australian Securities Exchange last week that it would have to downgrade 2019 production at its Pilbara iron ore operations by 13 million tonnes to between 320Mt and 330Mt. It had expected a 333Mt to 343Mt range.
The company blamed "mine operational challenges" for the downgrade.
Australia's Mining Monthly understands Rio Tinto is behind in mine development - mainly waste movement and general mine sequencing at Greater Brockman.
The issues have led to a review of mine plans.
Rio Tinto is not sure how much the downgrade will affect its costs. It plans to release that information in its quarter two operational review on July 16.
A BHP spokeswoman told AMM it would not be commenting on its plans around production until its next quarterly production review.
Iron ore prices have been running north of US$100 per tonne for the past few days.