The gold miner's share price dropped more than 14 per cent in afternoon trading after Tanzania's Second Committee alleged it under-declared revenues and tax payments over a number of years by tens of billions of US dollars.
Acacia denied the findings, which it criticised for "grossly [overstating] the value of the concentrates by more than 10 times".
"Acacia strongly refutes these new unfounded accusations. We have always conducted our business to the highest standards and operated in full compliance with Tanzanian law," the firm said in a statement.
As Tanzania's largest investor, a spokesperson for Acacia said the situation sets a terrible precedent for companies looking to invest there in the future.
The committee made a series of recommendations, including the payment of outstanding taxes and royalties, re-negotiation of large-scale mineral development agreements, government ownership in the mines and the continuation of the export ban.
The surprise ban is costing the firm $1m (£0.8m) a day, and its shares have fallen more than 40 per cent since the day it was announced.
Acacia said it remains open to further dialogue with the government, which it has long sought to partner with to achieve enhance social and economic development in the country.
"We will provide a further update to the market as soon as practical," the miner said.