Whiteduck accused the event's organizers of distributing fake cards to people who are not Native American and argued that the group is doing more harm than good.
"This letter serves notice that what you and your organization does is fraudulent and can cause more harm to legitimate Section 35 First Nations peoples in our territory," he wrote in a letter published to Twitter last week.
WHITE WOMAN CAUGHT LYING ABOUT HER RACE RESIGNS AS EQUITY AND INCLUSION
A "No Honor in Racism Rally" marches in front of TCF Bank Stadium before an NFL football game between the Minnesota Vikings and the Kansas City Chiefs, on Oct. 18, 2015, in Minneapolis. (AP Photo/Alex Brandon)
"The event taking place on our unceded lands is inappropriate and unacceptable," the letter continued.
"This is cultural appropriation," Whiteduck warned.
Whiteduck was first invited to speak at the event but declined. In his tweet, he labeled the group "wannabes."
NATIVE AMERICAN TRIBES DEPENDENT ON FOSSIL FUEL RESOURCES RIP BIDEN ADMIN FOR DOUBLE STANDARD
In this Friday, Jan. 18, 2019 image made from video provided by the Survival Media Agency, a teenager wearing a "Make America Great Again" hat, center left, stands in front of a Native American who approached him singing and playing a drum in Washington. (Survival Media Agency via AP)
"I wouldn't be caught dead at their events or anything [that's] a part of their association or group," he told CBC Tuesday.
In his open letter, Whiteduck asked the local government to "respect and adhere to" his group's concerns and called on officials to "distance" themselves but did not elaborate on what that would constitute.