The Liberal party has seen its fair share of nomination battles, and a fresh one is brewing in the Toronto-area riding recently vacated by former immigration minister John McCallum, who stepped down to begin his life as a diplomat.

This fight is being led by Juanita Nathan, a local school board trustee who put her name forward to be the Liberal candidate in Markham-Thornhill.

Nathan said she believes the Liberals are setting up the contest in such a way as to favour one of her rivals: Mary Ng, a senior staffer to Prime Minister Justin Trudeau.

"I don't think they are following the rules in a very fair and equitable way," Nathan said Monday.

The issue revolves around the cut-off date to register new Liberals — an important element of the nomination rules, because it determines who will be allowed to vote Saturday to choose the Liberal candidate in the April 3 byelection.

Nathan said more than 2,000 people she has registered as Liberals are considered ineligible because the party retroactively set the registration cut-off date for Feb. 14 — the day before she started entering names into the system.

The Liberals got rid of membership fees last summer, but those interested in taking part in nomination votes are still required to sign up to do so.

Ng's team says it lost registrants too

Setting a retroactive sign-up deadline is nothing new — parties do it routinely in order to prevent would-be candidates from waiting until the last minute and overwhelming officials with paperwork.

But the speed at which the process is unfolding — the deadline was set just four days after the call for nominations, at a time when Ng was the only one to have come forward — has made Nathan suspicious.

"I never thought there would be such a very, very short cut-off time," she said.

Another candidate, Nadeem Qureshi, shared similar concerns with the Hill Times newspaper. Qureshi confirmed Monday that he is running for the Liberal nomination, but did not otherwise respond to an interview request.

Amanda Alvaro, a spokeswoman for the Ng campaign, said her candidate learned of the deadline on Feb. 20, the same as everyone else.

"Our campaign also lost several hundred registrants," Alvaro said.

She said Ng, who is taking a leave of absence from her position as director of appointments in the Prime Minister's Office, began canvassing the residents of Markham-Thornhill in the days after the party opened the call for nominations on Feb. 10.

Rules online for months, says party

Liberal party spokesman Braeden Caley says the retroactive cut-off date was explained in rules that have been available online for months and that candidates are encouraged to turn in their new-member paperwork as early as possible.

"The party undertakes an extraordinary amount of effort to make sure that all of the rules are very openly and clearly communicated at every stage of the process," said Caley.

Jack Siegel, a lawyer who oversaw the approval of Liberal candidates leading up to the 2015 federal election, said the whole point of a retroactive cut-off date is to prevent candidates from overwhelming party resources by submitting names in bulk.

That's why he urged campaigns to turn their names in as soon as they get them.

"It's easy, when something goes wrong and you've made a strategic mistake, to portray yourself as a victim," he said, adding it ends up casting both the party and the successful candidate in a negative light.