THE CANADIAN PRESS -- Former Ontario Premier Bill Davis, former deputy prime minister Don Mazankowski and Senator Gerry St-Germain are endorsing a letter urging party members to keep their constitution intact.

The trio of Conservative elder statesmen is speaking out against a controversial proposal to change the federal party's constitution that threatens to overshadow this week's national convention.

The future strength of the party, the say depends on leaving a key element of its constitution intact.

The three men were emissaries for the Progressive Conservative party when it was in talks to merge with the Canadian Alliance in 2003. Ensuring that all riding associations were treated equally regardless of their size was the key condition of the Progressive Conservatives in the deal.

"We expressed clearly, and heard back just as clearly from our fellow negotiators, that this principle of equality of riding associations was not just a sine qua non of the union of our two legacy parties but also an important building block for the future success of our Conservative party," reads the letter.

The Conservative convention, which starts Thursday, has been billed as a three-day celebration of the electoral majority won by Prime Minister Stephen Harper on May 2. But the battle over the party constitution is shaping up to be a major side event.

Ontario MP Scott Reid was a negotiator for the Canadian Alliance, and has mounted a highly organized campaign to alter the party's constitution to give more weight to bigger riding associations. As things stand now, that would give a greater voice to party members in Ontario and western Canada.

The three eminences grises argue that proposal goes against the spirit of the current electoral system, in which ridings are all recognized as equal regardless of how many people live in them.

"As long as the goal of the Conservative Party of Canada is to elect Conservative governments, the principle of equality of electoral district associations and the discipline that it entails must therefore remain an integral part of our governance," the letter reads.

"To do any less would be to send exactly the wrong message to citizens who may consider supporting our party for the first time, or who many come from regions that are not our traditional area of strength."

Some Tories in Quebec have warned that Reid's motion would further alienate people in the province, who they say are already feeling abandoned by the party after a disappointing election campaign in which the party took only five Quebec seats. It is believed fewer than 100 Quebec delegates will attend the Conservative convention.

Supporters of the equality principle have mounted their own campaign to counter Reid's. Sources told The Canadian Press that several high-profile party members and MPs held a conference call Sunday night to discuss the matter.

They plan to put their own motion to the convention floor that would change the party's governance objectives to include the concept of equality of all ridings — essentially rendering any amendments to leadership rules moot.

Reid, meanwhile, is trying to fast-track his amendment so that it hits the floor of the convention directly rather than going through a committee process. To ensure this, he would need members from 100 ridings to sign a petition.

Last week, on the day MPs were electing the Speaker of the House, Reid handed out letters to all his caucus colleagues urging them to support his amendment which he has called a "compromise" position.

"The 'Balanced Leadership' formula that I am proposing takes the best elements of the systems used by our legacy parties, and merges them," Reid wrote.

"This system, if adopted, will ensure that all regions of the country have a strong say in electing the leader, but also that the leader has to win a legitimate majority of all votes cast. ..."

Other riding associations, including Immigration Minister Jason Kenney's, have proposed similar amendments that move the party closer to a one-member, one-vote system.

Reid's letter was sent on parliamentary letterhead, and emails sent about the party amendment have been sent from Reid's Parliament Hill office. The fax number provided for people to return signed petitions is also an office line.

The Board of Internal Economy by-laws, which govern the use of House of Commons resources, and the manual for MPs' allowances state that their operating funds are to be used for "parliamentary functions."

Prior to the election, a staff member with Immigration Minister Jason Kenney resigned after sending out letters about party matters from a Parliament Hill office.

"With regard to your inquiry regarding the use of the parliamentary email account and about 170 sheets of my MP letterhead for party business, I had not been aware that this is a violation of any Board of Internal Economy rules (or of any other rules, if it's the case that the Board does not have jurisdiction in this matter)," Reid wrote in an email, responding to questions about the use of parliamentary resources.

"Perhaps you know something that I don't about the relevant rules, in which case I invite you to enlighten me."

Reid went on to say he would stop using Commons letterhead and would be asking the Speaker if there was any rule he had broken. If so, Reid said he would repay the cost of the letterhead and use of the parliamentary email address.

The current Conservative party constitution awards each riding association 100 points during a leadership contest. Every member casts a ballot, and then points are awarded based on the percentage of members in the riding that voted for each contestant.