Kenney will meet with Wildrose leader Brian Jean at 3 p.m.in Edmonton Monday to talk unity.
"Today we are sending a message to the NDP".
In a statement Hallman called the event unfortunate and said he "regrets any inconvenience or upset that may have resulted from this incident".
His competitors, Vermilion - Lloydminster MLA Richard Starke and Calgary lawyer Byron Nelson, are painting a different picture for their vision regarding the future of PC's, aiming instead for a revitalization of the over century-old party.
"As I've said for 18 months, Wildrose has its dancing shoes on when it comes to creating a single, principled, consolidated, conservative movement", said Jean, who also left federal politics for provincial opportunities.
Kenney has stressed unity is necessary to avoid the vote splitting he says led to the majority win by Premier Rachel Notley's NDP in 2015.
Kenney said there is a lot of work ahead but if all goes well he would like a new party ready to go within a year.
"All I'm proposing is that we bring together two halves of a family that cohabited successfully and gave good government to Alberta for the better part of four decades, but fell apart a few years ago", said Kenney. Kenney's critics fear he will abandon the PC's centrist approach on social issues to embrace the social conservatism of the Wildrose.
Wildrose too will have to craft a merger-type policy - or a motion to wrap up the party altogether with the view to joining a new conservative force - and vote on it.
They booed Starke during his speech when he warned that a merger with the Wildrose could tar the PCs with the label of intolerance toward women and minorities.
Both Starke and Nelson said they will stay on to move the party in the right direction.
WATCH ABOVE: A brief history of the recent PC downfall: They were a political dynasty in Alberta but as Shallima Maharaj explains, with Jason Kenney at the helm and wanting to unite the right - the traditional Progressive Conservative party may soon cease to exist.
"We go straight into negotiations". I don't want to do that again to be honest, " said Jean.
The NDP immediately reached out to progressive voters on Twitter after Kenney's win.
Well, it may seem odd for an old Dipper to lament the passing of the PCs - Kenney backers would likely just say it's proactive sour grapes 'cause they're gonna win in 2019 and party like it's Saturday night at Mar-a-Lago.
"Progressives looking for a modern and moderate party?" There is no provision in the PC constitution to dissolve itself and the leader is just one vote on the party's board of directors.
We'll take Door No. 3.
Kenney did not put a number on what percentage of votes it would take to claim a mandate for unity during the coming referendum.
The PCs and Wildrose, should they join forces, would have just two years to create constituency associations and field candidates in time for the next election, set for the spring of 2019.
Elections Alberta says provincial parties are not legally allowed to merge, so Kenney is advocating a new party through a deal ratified by each party's membership.