The Conservative Senate leadership has kicked Nova Scotia Senator Stephen Greene out of the Tory caucus just hours before he was set to have dinner with Prime Minister Justin Trudeau.

Greene, who was appointed in 2009 by former prime minister Stephen Harper, said he was "ambushed" this morning during the Conservative Senate caucus meeting and "delivered with an ultimatum to leave."

The decision was made by the party's Senate leader, Quebec Senator Larry Smith, sources told CBC News.

'I was amazed, I was disappointed, I was crushed a little bit.' - Senator Stephen Greene

"I was asked to go upstairs to talk to the leader and I was informed I had to make a choice. If I went to the dinner, I'd have to leave caucus. And I said, 'Well, I want to do both," Greene said in an interview outside the chamber.

"But for some reason, just because I accepted a dinner reservation from the Prime Minister of Canada ... it was too much for the Conservative caucus.

"I'm a Conservative; I was Preston Manning's chief of staff a long time ago ... and I'm Maxime Bernier's Nova Scotia campaign chair. I'm a Conservative, and I always have been, and this won't stop me from being a Conservative," he said.

Senator removed from Conservative caucus6:53

Trudeau and Peter Harder, the government's representative in the Senate, had invited all senators who introduced government legislation in the upper chamber to a dinner Tuesday night to thank them for their efforts.

Greene is the only Conservative to sponsor a government bill during this parliamentary session.

He helped usher through Bill S-4, a rather innocuous piece of legislation that enacted a double taxation agreement with Taiwan and Israel. Greene said he sponsored a nearly identical bill on a similar matter during the Harper years.

'Follow a certain line'

For his part, Smith said Greene has cast votes at the Senate modernization committee — tasked with studying the future of the Red Chamber in an era of greater independence — that would effectively dismantle the Official Opposition.

"When you have a Liberal prime minister who invites a supposedly Conservative member to his house … we're just very concerned about that," Smith told reporters Tuesday. "If he was going to cross the line, which is basically supporting a lot of the Liberal government's policies, then he doesn't really belong in the Conservative group.

"We want to make sure our members follow a certain line."

Conservative sources, speaking on background, said Greene has not been a "team player" in recent months and has been too "buddy-buddy" with Harder and other Independent senators. The former Conservative Senate leader, Claude Carignan, also tried to force Greene out, the sources said, because he was straying too far from the party line.

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Senator Peter Harder, the Trudeau government's representative in the upper chamber, says Greene has long had an independent streak. (Adrian Wyld/Canadian Press)

Greene also endorsed Harder's idea to create a Senate business committee to draw up a schedule and hash out appropriate time limits on debate in the Red Chamber.

Harder has complained about use-of-delay tactics that stall the progress of government legislation. But opposition members have said such a committee would stifle efforts to hold the government to account.

Greene has long had an independent streak, Harder said Tuesday, pointing to a report he authored with Liberal Quebec Senator Paul Massicotte in 2015 that called for an end to "institutionalized partisanship" in the upper house.

"He's clearly wanting to support a less partisan, more independent Senate and I welcome it," Harder said.

Greene recently ran as a candidate to replace Claude Carignan as leader of the Conservative caucus in the Senate but ultimately lost out to Smith.

'Treasonous'

"I was amazed, I was disappointed, I was crushed a little bit. The words betrayal and treason and treasonous were also used," Greene said of Smith's ultimatum.

Greene said he offered to give the Conservative leadership a "bird's-eye view" of what happened at the dinner meeting, and report back to his fellow Tories, but was rebuffed.

"I would go to dinner with any prime minister who invited me," he said. "This whole situation is beyond silly. Would my Senate leadership not want me to attend such a dinner so that I can report back on what the Liberals' plans are for the Senate? It makes no sense."

Greene said he will now sit as an "Independent Reform senator," a name he crafted this afternoon with his office staff, which references his past allegiance to the defunct Reform Party of Canada. He will sit on the other side of the chamber alongside members of the Independent Senators Group and Liberal Senators.