Joan Jessome of the Nova Scotia Government and General Employees Union said the government's move will result in nurses seeking employment in other provinces as it fails to address staffing issues.
The 2,400 nurses represented by the union can legally go on strike Thursday. The union wasn't able to say how many nurses didn't show up for work and a spokesman for the Capital District Health Authority couldn't be reached for comment.
The impact of a strike by nurses in Halifax stretches beyond the city as its hospitals serve as a regional health centre.
Patients are treated at Halifax hospitals from across the Maritimes. Last week, Prince Edward Island began moving some patients back to their home province.
Outside the legislature Tuesday, nurses protested against the introduction of the Essential Health and Community Services Act.
The legislation would require unions and employers throughout the health-care sector to have an essential services agreement in place before strikes or lockouts start.
Members of the legislature debated the bill overnight.
The union, which filed strike notice hours before the legislation was introduced, has agreed to maintain emergency services.
Jessome said the legislation introduced by the province's Liberal government weights collective bargaining in favour of employers.
The union and the health authority have been unable to come to an agreement despite the help of a mediator.
Late Monday night, Capital Health said on its website that mediated talks ended in an impasse. A spokesman for the health board said earlier Monday that as the strike deadline approaches, it was cancelling surgeries and transferring patients to hospitals outside the city.
The key sticking point in the dispute is a demand from the union to increase nurse-to-patient ratios, something it says would improve patient safety. The health authority has said there is no evidence that mandated ratios guarantee better safety.
Before the bill was introduced Monday, Premier Stephen McNeil said three labour disruptions in the health-care sector within seven months underscores the need for a law.
"This is about striking a balance between ensuring that Nova Scotians have the services when they need them while protecting the workers right to strike," he added.
Labour Minister Kelly Regan said Nova Scotia was the only province without this kind of legislation.
In addition to nurses, the bill would apply to paramedics, 911 operators, hospital employees and people who work in homes for seniors, youth and people with disabilities. In all, about 35,000 to 40,000 workers would be covered by the law.
The essential services legislation would also allow parties to request conciliation or mediation to help negotiate an essential services agreement. If they can't agree, either party could apply to the Nova Scotia Labour Board.