Earlier this week, 10 Progressive Conservative riding association members filed motions seeking a review of Hudak’s leadership at next month's policy convention in London, Ont.
They were upset after the party lost four out of five byelections on Aug. 3.
MPP Frank Klees, who finished second to Hudak in the leadership race in 2009, said the PC leader should allow the review.
PC deputy leader Christine Elliott, who finished third in the 2009 race, spoke out against it.
'We're not going to back off'
Now riding association members are feeling the heat after speaking out against their leader.
"(There have been a) number of phone calls telling us to withdraw, from party officials and some cabinet members," said Cheryl Miller, one of the 10 who called for a review.
"It's become a firestorm and it's pitted PC against PC."
Miller would not divulge the names of people who called her and her colleagues, other than to say they hold senior positions within the party. But she said the threats would not intimidate the group.
"I think it's just firmed up our resolve. We're not going to back off. We're going to follow this right through," said Miller.
Klees, Hudak have history
Klees told CBC News said the reports of harassment and alleged threats are "highly offensive."
"The kind of dramatics being carried out is something they should apologize for. And for the party to reduce itself to this kind of intimidation is not the party I joined," Klees said.
Klees and Hudak have had some public disagreements over the past few years. When Klees lost a bid in October 2011 to be the speaker at Queen's Park, Hudak spoke out against the MPP's run for the job.
At the time, Hudak said he offered Klees two prominent critic portfolios to keep him in the opposition benches but was turned down. Klees said his decision to run for speaker did not reflect dissatisfaction with Hudak or the party.