Members of the group say they have outstanding questions about automated phone calls they received, directing them to incorrect polling stations on May 2, 2011.
The letter is addressed to Canada's chief electoral officer as well as the commissioner of Elections Canada.
The agency laid a charge against one person, Michael Sona, following the robocall campaign that played out in Guelph.
The Ontario Court of Justice convicted Sona of wilfully preventing or endeavouring to prevent an elector from voting.
The former Conservative staffer is currently serving a jail sentence of nine months.
The letter to the agency was signed by 26 people who say they do not have "any confidence in Election Canada's ability" to protect personal information.
"The impact of this tactic is unknown but at least one elector did not vote as result of it," the letter states. "Others tore up their voter information cards."
The note also calls for the agency to re-open its investigation in other cities where voters say they received misleading robocalls.
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