The Southern Chiefs' Organization has until Friday to explain $261,587 in expense claims to the federal government.

In a letter obtained by the Canadian Taxpayers Federation, the federal Aboriginal Affairs and Northern Development Department outlines numerous questionable expenses that were filed between 2010 and 2013.

The expenses in question include the unauthorized use of a debit card used by former grand chief Murray Clearsky and his chief of staff, retroactive pay increases, payroll advances, travel claims to Las Vegas and Minneapolis, and almost $48,000 in expenses for traditional healing purposes.

The department's letter, dated July 25 and addressed to current Grand Chief Terrance Nelson, says if SCO cannot explain these expenses, the organization will have to pay them back.

Calls to the Southern Chiefs' Organization have not been returned as of midday Thursday.

A spokesperson for the Aboriginal Affairs Minister Bernard Valcourt told CBC News that First Nations chiefs, councils and organizations are accountable to their members.

"To ensure federal funding is being used for its intended purposes, funding agreements between Aboriginal Affairs and funding recipients include a 'right to audit' clause," the spokesperson wrote in an email.

"The Government of Canada is conducting a forensic audit of SCO. Should AANDC find indications of criminal wrongdoing, the information will be turned over to policing authorities."

In October 2013, the organization removed Clearsky as its grand chief after allegations surfaced that he misused funds at a casino and amusement park in the United States.