Former Sinn Fein TD Peadar Toibin has said the party should reveal the voting breakdown in its vice-presidential election in the interests of transparency and democracy.
Upper Bann MLA John O'Dowd failed to unseat Michelle O'Neill for the number two position in the party.
Voting took place by secret ballot at the party's ard fheis in the Millennium Forum in Londonderry last weekend but Sinn Fein is refusing to make public Ms O'Neill's margin of victory.
There are unconfirmed reports that the Upper Bann MLA polled strongly.
Sinn Fein said it will be reviewing its party processes regarding internal elections.
Mr Toibin said public confidence in the party would be undermined if there wasn't transparency in future.
The Meath West TD split with Sinn Fein over abortion, and in January formed his own party, Aontu, which is contesting seven Westminster seats in next month's election.
Mr Toibin said that Sinn Fein should move to facilitate greater internal democracy and that Mr O'Dowd should not be sidelined for his challenge.
The Aontu leader said: "Any party leadership contest should be entirely transparent. By not disclosing how many votes Michelle O'Neill and John O'Dowd each received, Sinn Fein is reducing public confidence in politics."
Mr Toibin, who was a Sinn Fein member for 21 years, said the party needed to change.
"There are internal mechanisms for democracy in the party but they're not used.
"Instead, democratic centralism prevails when it comes to decision-making," he said.
"Both John O'Dowd and Michelle O'Neill should have had a platform to set out their vision of republicanism for the next 20 years. But neither got the opportunity to do so.
"It is also clear that the leadership came down very heavily in favour of Michelle O'Neill during the contest."
Mr Toibin said that Sinn Fein needed to "consult and trust its membership more" on the direction of the party in future.
"Sinn Fein's iron discipline was a strength before and during the peace process. But it's now a distinct disadvantage which is damaging the party," he said.
"There should have been transparency during the vice-presidential contest. In a democracy, transparency is a threat to nobody.
"I would hope John O'Dowd isn't sidelined in the party as a result of his challenge.
"The party should facilitate internal democracy. Otherwise, there is a danger that members who aren't able to vent their frustration just walk."
When asked if Sinn Fein was considering a review of its processes which may mean internal election results are made public, a party spokesperson said: "Sinn Fein regularly review our party processes."
Mr O'Dowd congratulated Mrs O'Neill after the result was announced on Saturday, saying in a tweet that he looked forward to working with her in the future.
He also thanked those who had supported and voted for him in the contest.
His challenge for the position was revealed by this newspaper two months ago.
Mid Ulster MP Francie Molloy was critical of the move and said the timing was wrong for a leadership challenge, while Fermanagh-South Tyrone MP Michelle Gildernew threw her support behind Mr O'Dowd.
TUV leader Jim Allister branded as "totalitarian" Sinn Fein's failure to reveal the breakdown of the leadership vote.
"What have they got to hide?
"Why not release them?
"I have always thought they were totalitarian in their approach - and this has proved it as far as I'm concerned," he said.
But Sinn Fein has defended how it conducted the election contest.
A spokesperson said: "With almost 400 cumainn (branches) and 60 comhairli ceantair (district councils) across the island it was deemed impractical to organise hustings for the position of leas uachtaran (vice-president).
"All candidates were afforded the opportunity to distribute material to all party structures and to speak with all ard fheis delegates."
The spokesperson added: "Representatives of the two candidates for the position of leas uachtaran were present at the counting of the votes."