Treasury Board President Scott Brison will repeal changes the Harper government enacted that made it more difficult for federal public servants to strike by expanding the definition of what constitutes an essential service.

"As another important step in rebuilding the relationship with Canada's public service, we are moving to repeal changes to the public service labour relations regime brought into law by the previous government," Brison said in a statement Wednesday, noting the legislation will be introduced in the fall.

The 2014 budget omnibus bill made it illegal for any federal bargaining unit to strike if 80 per cent or more of the positions in that unit are declared necessary for providing an essential service.

The legislation also allowed the government to define what exactly an essential service is, and how many positions are required to provide that service. Unions feared that the government would use these new powers to raise the number of workers deemed essential and remove their ability to strike.

Prior to the legislative change, an essential service was strictly defined as anything necessary to ensure the safety and security of Canadians, including food inspection, correctional officers, border security, search and rescue and marine safety, among other positions.

The Public Service Alliance of Canada (PSAC), the largest union representing federal public servants, filed an Ontario Superior Court challenge against the legislation in 2014.

Clement opposes change

The union has argued the legislation undermines the constitutional rights of federal public service employees to collective bargaining, as it would undermine their right to strike. "The designation of employees under the act is so extensive that it renders the freedom to associate and strike meaningless," the union wrote in its court filing.

"I disagree with the way that the public sector unions termed the legislation, and I disagree with the repeal of the legislation," said former Conservative Treasury Board President Tony Clement, who spearheaded the law when it came in.

"The legislation was designed to protect the public interest, to make sure that it aligned with what were considered to be essential services and the way that the design of the act, and certainly my practice was, to always consult with the unions before we designated something essential," he said.

Clement said because the legislation was designed to work in consultation with the unions, he is confident no court would "uphold a situation where a government would unilaterally declare huge swaths of the public service essential and therefore deny them the right to strike."

Tense collective bargaining over sick days

Brison's announcement comes amid ongoing negotiations between the federal government and PSAC to hammer out a new collective agreement.

The minister had been non-committal on repealing the essential services definition — saying only that the government would study the issue — until now.

The union welcomed the promise to enact new legislation Wednesday calling it a "correction" to "some of the harm done by the Conservatives."

"PSAC has asserted that Bill C-4 is an attack on our members' fundamental charter rights and not consistent with a free and democratic society. Our members worked tirelessly to lobby members of Parliament about the injustices of this bill. I want to thank them for their continued vigilance," PSAC national president Robyn Benson said in a statement to CBC News.

But the biggest sticking point between the government and the 18 unions that represent public servants is sick leave benefits. Brison has already tabled legislation in the House that reverses some of the unilateral changes the former government made to sick leave benefits.

The Liberal government is still seeking to "modernize" the program, but the unions are against any changes to the current system, which allows workers to bank their sick days.

The latest move comes after the Liberal government tabled legislation in January that repeals two other Conservative changes to the laws that govern labour unions, including Bill C-377, which requires unions to disclose how they spend members' dues, and Bill C-525, which makes it harder for unions to organize in federally regulated workplaces.

"By restoring fair and balanced labour laws, the government is recognizing that labour unions play an important role protecting workers' rights and strengthening the middle class," Brison said.