Tony Clement is defending plans to wait until after the latest budget bill becomes law before fully detailing how Ottawa will block some public servants from going on strike.

The President of the Treasury Board is at the centre of controversy this week after the Conservative government tabled a budget bill that includes sweeping changes to federal labour laws and procedures.

The legislation would give the employer the exclusive right to declare jobs as essential services where workers could not strike, removing unions from that decision. It would also limit the role of arbitration for resolving disputes. Arbitration would be allowed only in cases where bargaining units have 80 per cent or more of their positions designated as essential, or if both parties mutually consent to binding arbitration.

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In an interview with The Globe and Mail, Mr. Clement played down concern these powers would be used arbitrarily. He said unions would be consulted, but the government will have the final say. "Ultimately we believe the decision to protect the public is the government's decision. It's not a negotiating point that can be traded off for other things with the unions," he said.

The minister said he can't offer details on what kind of jobs would be declared essential or the expected percentages for each department.

"You can't start really implementing a bill until it's actually passed by Parliament. That's the reason why that has to wait," he said. "For observers and commentators, I'm sure they can figure out what's essential and what's not essential."

The minister was criticized in the House of Commons and on social media for refusing in a Thursday morning radio interview to answer questions about who would be declared essential.

"I am waiting for this legislation to pass and then details will come forward," he told CBC radio host Robyn Bresnahan on a local Ottawa program. Ms. Bresnahan had told the minister that the station had received a lot of negative feedback about the changes from the regions' public servants. The interview turned tense at times, with Mr. Clement flatly refusing to answer some of the host's questions.

The legislative changes are contained in Bill C-4, which introduces provisions from the March budget and includes a section that affects Canada's labour relations with federal public servants.

The government's budget bill was first introduced on Tuesday. On Thursday morning, the Conservative majority voted through a time allocation motion on the budget. As a result, second-reading debate will be limited to four more days before it is sent to committee for hearings.

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The Canadian Labour Congress issued a statement Thursday calling the bill " an attack on the constitutional right to collective bargaining" and accused the government of trying to hide the changes in a budget bill.