OTTAWA — The country's top court has declared that the Crown can renege on a plea bargain that would have allowed a woman to plead to careless driving in a deadly crash.

The Supreme Court of Canada was unanimous in its decision, the first time the justices have ruled on the discretion allowed prosecutors in plea agreements.

The Alberta case involved Olga Maria Nixon, who was charged with impaired driving causing death and injury in a 2006 crash which killed a couple and injured their seven-year-old son.

A prosecutor concluded there were problems with the admissibility of the breath samples and agreed to reduce the charges to dangerous driving causing death and injury.

Further negotiation led to a deal for a plea of careless driving, a traffic offence.

However, the attorney general's office determined that agreement was contrary to the administration of justice and withdrew it.

Nixon's lawyers then argued that the Crown's repudiation of the deal was a violation of her Charter rights. The trial judge agreed and ordered the Crown to proceed with the lesser charge.

The Alberta Court of Appeal disagreed, and the Supreme Court of Canada upheld its decision.