Liberal Party executive director Mike McDonald said Monday the party did not support Slater's candidacy in his Boundary-Similkameen riding, and is moving quickly to find a new candidate.
McDonald said the party has been in discussions with Slater for months, but was recently forced to act after Slater indicated he wanted to run again under the Liberal banner.
"It's an exceptional situation, and this is not something we take lightly," McDonald said. "We try to deal as discreetly and respectfully as possible. This is the last thing we want to see, getting into a situation like this."
But he said the Liberals decided it had to put the best interests of the party and Slater's constituents first when it refused to let Slater run for the Liberals.
Party President Sharon White said in a statement Slater's candidacy was not approved because of his personal issues and the party feels those issues would impact his ability to represent the Liberals.
White's statement did not identify the personal issues, but said Slater told the party last month he would not seek re-election, and only recently changed his mind.
"Mr. Slater’s candidacy is not being approved due to personal issues that, in our view, impact his ability to represent the party," said the statement.
White's statement said the party tried to work out a solution with Slater, and the decision wasn't taken lightly.
Slater acknowledged he has personal issues, but suggested he may also have ruffled feathers with his candid opinions on Liberal issues, which he regularly expressed behind closed doors.
"Basically, they are saying I can't win the riding, so they'll get somebody who can," Slater said. "There were some times where I'd state my mind against some party policies, that's part of it too, I think."
He said he didn't want to discuss his battles within the party even though he's now out of the party.
Slater said there were other personal issues, of which he would not elaborate.
He said he consulted his doctor last spring after he was observed swaying down a hall at the legislature on his way to a caucus meeting.
Slater said Monday a combination of prescription medication, antihistamines and a glass of wine left him out of sorts for much of the afternoon.
Liberal officials kept Slater in the party caucus room for several hours after which he emerged and said he was discussing rural issues with party brass.
The current party standings now are, Liberals 45; New Democrats 36, and four Independents.
Slater's Liberal MLA website was deactivated shortly after the party announcement.
But on his personal MLA home page, Slater said he is proud to serve the citizens of his Osoyoos-area riding in the south Okanagan.
"We define our lives by what we give back and I have never taken for granted the trust that people have placed in me," he said. "My service to the community through my many volunteer activities has been deeply gratifying. I have found no greater reward than when working together to achieve that which cannot be achieved alone."
Prior to being elected in 2009, Slater was a veteran municipal politician, including serving six years as the mayor of Osoyoos.