Hundreds of nurses formed picket lines outside most Halifax-area hospitals this morning. Here's what you need to know about the strike and what led to it:

How will the strike affect you?

The Capital District Health Authority says for routine care and non-life-threatening medical conditions, you should call your family doctor.

You can also get general health-care advice from a registered nurse by calling 811.

For emergency health care, you should go to your nearest emergency department of call 911. The emergency department will be fully staffed during the nurses' strike.

If your surgery or appointment is postponed due to the strike, Capital Health says you will be called to arrange a time to reschedule. If you haven't been called by Capital Health and told otherwise, your surgery and clinic appointment are going ahead as scheduled.

All emergency departments, dialysis units, Nova Scotia Cancer Centre and intensive care units are open.

Who has been affected so far?

In the Capital District Health Authority, 208 surgeries have been cancelled this week — 188 at the Queen Elizabeth II Health Sciences Centre and 20 at Dartmouth General.

Health authorities outside of the Halifax region have also cut services to their own patients as they anticipate taking patients from Capital Health.

Who's involved?

The ongoing contract dispute is between the Capital District Health Authority — Nova Scotia's largest health authority — and the Nova Scotia Government and General Employee's Union Local 97.

Local 97 represents 2,400 registered nurses who primarily work at the Queen Elizabeth II Health Sciences Centre, the Nova Scotia Hospital, the East Coast Forensic Hospital and Public Health Services.

This dispute does not include members of the Nova Scotia Nurses' Union, which represents another 6,700 registered nurses, nurse practitioners and licensed practical nurses working in hospitals, long-term care and community care facilities across the province.

What do they want?

The Nova Scotia Government and General Employees Union is demanding higher staffing levels to ensure patient safety. The union wants a mandated ratio of one nurse to every four patients, implemented over time.

The Capital District Health Authority has said the demand for nurse-to-patient ratios won't work because it is too inflexible and there is no evidence it would improve safety. They claim the staffing levels proposed by the union would require hiring 800 more registered nurses at an annual cost of more than $60 million.

When did it all come to a head?

Contract talks between the two sides broke down in mid-March. A mediator was appointed to assist the talks but after a series of negotiations, the two sides reached an impasse on Monday evening.

That same night, the Nova Scotia government introduced essential services legislation.

The Nova Scotia Government and General Employees Union had said the introduction of such legislation would result in "immediate strike action."

That's exactly what happened the next day — 140 registered nurses failed to show up for scheduled shifts, forcing the cancellation of dozens of surgeries and inflaming tensions between the two sides.

It was an illegal strike because the members were not in a legal strike position until Thursday at 12:01 a.m.

Later on Tuesday, the Nova Scotia Labour Board issued a cease and desist order and the union asked its members to report for their next scheduled shifts.

What is essential services legislation?

When the law is passed, nurses and other health workers will first have to agree with management which positions are essential services and staff those positions before starting any strike action.

The Nova Scotia Government and General Employees' union says such deals can take up to six months to reach, effectively taking away their right to strike in that time.

Premier Stephen McNeil has said the new law is needed because there have been three labour disruptions in the health-care sector within seven months — paramedics, home-care workers and now registered nurses.

The legislation would apply to nurses, paramedics, ambulance dispatchers, 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.