There was more trouble Thursday within Manitoba's New Democratic Party as a key labour leader accused two party officials of interfering in the party's upcoming leadership race.

Interim leader Flor Marcelino and NDP president Ovide Mercredi issued a letter to party members that touts the benefits of allowing every party member a vote.

The party has traditionally used delegates from each constituency and labour group.

"It's unheard-of for an elected president or leader to insert themselves at this stage," said Kevin Rebeck, president of the Manitoba Federation of Labour and a member of the NDP provincial council.

Rebeck recently co-chaired a NDP committee that examined the issue and proposed specific rules for both the delegate and one-member-one-vote systems. The committee recommended that the decision on which system to use be left to the annual convention in March.

That idea was approved by the provincial council, which Marcelino and Mercredi sit on.

"I'm pretty shocked that a letter would come out from our party president and leader who were part of a democratic process and decision, and it would come out against that democratic process and decision," Rebeck said.

Mercredi said he simply wanted to get the debate started and see if some consensus could be reached before the annual convention on party rules. The leadership convention is scheduled for September.

"Taking sides is part of the reality of politics," Mercredi said. "Everybody takes sides and all I'm saying is that we have to find a compromise."

The NDP has had internal battles since the fall of 2014, when five senior cabinet ministers challenged the leadership of then-premier Greg Selinger. Selinger survived the attempted coup and stepped down as leader after the NDP lost last April's provincial election.

Marcelino has repeatedly said the party remains divided, and factions that supported Selinger and his opponents have much work to do to reunite. Selinger remains in the NDP caucus and some of his supporters, including Marcelino and Mercredi, hold key roles.

Marcelino and Mercredi's letter, obtained by The Canadian Press, criticizes the delegate system as "far more exclusive, restrictive" than allowing every party member a vote.

The letter also criticizes specific delegate-system rules proposed by Rebeck's committee that would limit the number of delegates in constituencies with large membership numbers, such as The Pas and The Maples.

"These are constituencies that reflect the strong support our party has received from indigenous peoples and multicultural communities," the letter states.

"We cannot afford to have the focus on the convention be on divisive proposals to restrict our leadership selection process and be perceived as targeting the influence that indigenous peoples and multicultural communities have had in previous leadership contests."