Steven Taylor of the Blogging Tories has the documentation of the alleged voter suppression. (the fake letter is based on this)

A few weeks ago during a leadership campaign debate Frank Klees (MPP Newmarket-Aurora)  made a statement he had signed up 10 thousand members for the Ontario Conservative Party.
The leadership race took a turn last week when candidate Tim Hudak (MPP Erie-Lincoln) accused the Klees camp of push polling.
The party dismissed the complaint.

Today was the last day for 40 thousand party members to vote for a leader who will be announced Saturday at the convention. The Progressive Conservatives currently hold 24 of the 107 seats as Ontario’s official opposition.

Globe and Mail:

Progressive Conservative Party president Ken Zeise has asked the Ontario Provincial Police to investigate a letter that was mailed to some members of the party, warning them that the RCMP was conducting its own probe into allegations involving voter fraud in provincial party leadership contests.

The letter is clearly “bogus,” Mr. Zeise said in an interview on Thursday. And while the letter was sent by someone with access to the names and addresses of party members, Mr. Zeise said he has no evidence to suggest that a party member was behind it.

He said he called in the OPP after officials representing two of the leadership hopefuls – Christine Elliott and Frank Klees – formally complained to him and asked him to investigate the matter.

Sean Morley, the agent for Ms. Elliott’s campaign, says in a letter dated June 20 that the correspondence sent to party members contains “misleading and patently untruthful” statements.

“I am sure you will agree this is a deplorable piece of correspondence and its distribution is an attempt to intimidate a targeted group of party members,” Mr. Morley says in his letter.

Ontario PC Party

Christine Elliot MPP – Whitby Oshawa
Tim Hudak  MPP - Erie-Lincoln
Frank Klees MPP – Newmarket Aurora
Randy Hillier MPP - Lanark—Frontenac—Lennox and Addington

The Shotgun Ontario PC leadership policy summary