The Australian Taxation Office has conceded defeat in its $1 billion-plus tax dispute with Alcoa following a six-year battle with the US aluminium giant.

The ATO has declined to appeal a tribunal ruling against it, effectively ending the case, and will now be required to pay Alcoa $107 million in tax refunds. The defeat is a blow for Canberra, which is fighting to recoup billions of dollars in alleged unpaid taxes from several big US companies.