Fortescue Metals Group has been accused of "routinely" failing to honour its agreements with an important traditional owner group and of withholding millions of dollars in royalties.

The Wintawari Guruma Aboriginal Corporation (WGAC) said Fortescue had refused to pay $1.9 million of royalties that were due at the end of January unless the traditional owner group gave its blessing to the miner's request for nine mining leases.