Nova Scotia MP Peter MacKay says he never imagined a Conservative colleague from the province would vote against his government's budget, despite earlier saying the party's MPs were free to do so.

The foreign affairs minister faced questions from reporters in Halifax on Thursday, two days after fellow Nova Scotia MP Bill Casey was kicked out of the Conservative caucus for breaking rank on the budget vote.

"There is a Westminster tradition that members who vote against a money bill … can not remain in the party," MacKay said.

"I was confident that Mr. Casey and all members of the Atlantic caucus believed so strongly in the process we were following to see that the Atlantic Accord was respected that it would never come to this."

Before the vote, MacKay told the House of Commons that his party would not be "whipping, flipping, hiring or firing" any of their members for opposing the bill.

Casey, who represents Cumberland-Colchester-Musquodoboit Valley, was the only Conservative MP to vote against the budget.

He criticized the government, saying the Conservative budget doesn't honouring a promise to let Nova Scotia keep its offshore oil revenues and full equalization payments.

Prime Minister Stephen Harper defended his budget Thursday, saying it protects the 2005 offshore agreement and gives the province $95 million more than the deal offered.

The budget offers Nova Scotia a choice:

  • A new, enriched equalization formula that includes a cap on the amount of offshore oil and gas revenues the provinces can keep.
  • The old equalization formula, with the benefits from the Atlantic Accord on offshore oil and gas revenues that was negotiated by the former Liberal government in 2004.

Harper, in Germany for the G8 summit, was asked by reporters what he thought of Casey's decision to vote against the budget.

"I think you could guess my opinion on that," he said. "I don't think you really needed to ask."

Casey supported the budget in earlier votes, Harper said.

"Obviously, I don't think much of him changing his vote the fifth time."