The Supreme Court of Canada has decided to hear a case concerning the so-called "two beer" defence for alleged drunk drivers.
Ontario's Court of Appeal found last year that a change in legislation that put a greater onus on people charged with the offence of driving over 80 - referring to the legal limit of blood alcohol concentration - applies to cases in the system before the law change.
As is standard practice, the Supreme Court did not give reasons for agreeing to hear the case.
The case raises the broader issue of whether people already facing charges have to abide by a new rule brought in by Parliament or if they get the benefit of the rules as they stood when they were charged, said lawyer Paul Burstein.
"With our Conservative government passing more and more new criminal legislation faster than you can shake a stick at, obviously it's something that is an important principle to settle," he said.
Mr. Burstein, who is the defence lawyer for this Supreme Court appeal, said standard practice is that if a new law makes substantive changes it doesn't apply retroactively. But if it makes changes to procedural or evidentiary rules, it applies to cases already in the system from the moment it is passed.
"But sometimes it may look and sound like a procedural or evidentiary amendment, but in fact it operates more like a substantive change to the law," Mr. Burstein said.
Before July 2, 2008, someone charged with driving with a blood-alcohol content of more than 80 milligrams in 100 millilitres of blood could testify they had just two beers and have a toxicologist testify that wouldn't be enough to give a reading of over 80.
A Criminal Code amendment changed the law to require an alleged drunk driver to prove the machine was malfunctioning or was operated improperly.
The Crown is arguing that's a procedural change, and the defence is arguing it's substantive, because an accused's testimony that he or she didn't drink as much as the machine claims wouldn't be enough to potentially secure an acquittal, Mr. Burstein said.
Even in a murder trial if an accused provides logical, compelling testimony, it may be enough to provide a jury or judge with reasonable doubt about scientific evidence, he said, calling this amendment "extremely unique in criminal law."
But Andrew Murie, chief executive officer of MADD Canada, said what was happening before the amendment was that people were making a "mockery" of the system, beating drunk driving charges simply by saying they only had two beers and getting a few buddies to testify to it as well.
Mr. Murie said if there was a problem with the equipment or doubt about the blood samples, then by all means the defendant is entitled to a finding of not guilty. But if several tests show someone's blood alcohol level was over the limit and they say otherwise, the onus should be on them to prove a problem with the testing equipment.
The man at the centre of this case, Samuel Dineley, was charged with impaired driving and driving over 80 on July 21, 2007, and was acquitted a year later.
The Crown appealed but that judge held that cases in the system before July 2, 2008, could use the old law, the so-called Carter defence. The Crown appealed that ruling and the Ontario Court of Appeal granted it in November, 2009.