An organized-crime investigation involving prominent Melbourne harness-racing owner Paul Sequenzia has led to almost $6m tax bill.

Paul and his brothers Ricky and Daniel were hit with about $2m tax bill each in the past two weeks and were suspected of failing to declare income.

According to Justice Minister Michael Keenan, a national scheme that targets unexplained wealth of crime groups will be formed and could be finalized in weeks.

The scheme, which would prevent criminals from reinvesting their illegitimate profits, will be discussed at the Law Crime and Community Safety Council meeting in Canberra in November and could be in operation by the end of the year.