Robert McCorkill died in 2004, leaving $250,000 in artifacts and investments to the National Alliance, a white supremacist group in the United States.
McCorkill's sister, Isabelle McCorkill, wants the will quashed and filed an injunction last month.
When the matter goes to court in September, two prominent Jewish groups and the provincial attorney general will join her side.
Anita Bromberg is the head of legal affairs with B'nai Brith Canada — one of three groups granted intervener status in the McCorkill case.
She said neo-Nazi beliefs are on the rise in Europe and a six figure gift to the National Alliance could breathe life into the movement here.
"There's still an attraction to this philosophy, and to revive it is a dangerous concept," she said.
B'nai Brith will be joined by the Centre for Israel and Jewish Affairs, another of the interveners.
Richard Marceau, the general counsel for the Centre for Israel and Jewish Affairs, shares Bromberg’s concerns.
"The National Alliance is much weaker than it was in the past and we don't want to take any chances of money breathing new life into it," he said.
The province of New Brunswick, represented by the attorney general, will also have standing at next month's hearing.
All the interveners will be able to make submissions, trying to convince the court to wipe away McCorkill's will.
The lawyer representing the interests of the National Alliance did not object to any of the group's weighing in.
Rare coins, ancient weapons collection
The collection includes Greek and Roman coins that are thousands of years old, an ancient Iranian sword, Neolithic arrowheads and an Egyptian stone tablet from the 13th Dynasty, according to a 55-page appraiser's report from August 2010.
McCorkill was born in 1937, the son of a farmer in Bearbrook, Ontario.
He became a chemist and lived in Saskatoon in the 1990s, when he joined the National Alliance.
The University of Saskatchewan's Museum of Antiquities was lent a portion of his coin collection and put it on display for several years.
When McCorkill moved to Ottawa around 2000, he took his collection with him. Some of his artifacts remain on loan to the University of Ottawa's Museum of Classical Antiquities.
He's buried in Saint John's Fernhill CemeterySuggest a correction