Two leaders of a fundamentalist sect that condones plural marriage have pleaded not guilty to polygamy charges in a Cranbrook, B.C., courtroom where an epic battle to test the limits of religious freedom in Canada is playing out.

Well-known Canadian polygamist Winston Blackmore, 61, and his former brother-in-law, James Oler, 53, each face one count of polygamy under Canada's 127-year-old polygamy laws.

Their trial got underway today in B.C. Supreme Court, where Oler refused a lawyer and Blackmore refused to acknowledge the charge against him, forcing the court to record a not guilty plea for him.

Two young girls of the polygamous community of Bountiful walk past the mountains at Bountiful near Creston, B.C., in April 2008. (Jonathan Hayward/Canadian Press)

The two former bishops of the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS) are descendants of the original founders of the 1,500-person rural B.C. enclave, called Bountiful, where plural marriage has been practised for 70 years by the splinter group of the Mormon Church.

Blackmore at one time was the leader of the sect. Oler was appointed to lead Bountiful following Blackmore's excommunication from the Mormon splinter group in 2002 by Warren Jeffs, who was then the American FLDS leader.

He and his brother-in-law had a falling out and no longer speak. The two men lost a bid to be tried separately.

Oler is on trial for allegedly marrying four women between 1993 and 2009.

Unlike Blackmore, he's kept quiet about his actions, refusing interviews.

Blackmore does not deny he's had 24 wives over a 25-year period, and produced 145 children.

In previous Federal Tax Court hearings he forgot to name one of his wives, and admitted he'd need to call home for help to be able to name all of his offspring.

The legal battle dates back to the 1990s when investigations of the isolated religious sect were prompted by allegations that Bountiful residents were involved in multiple-wife marriages, described as "celestial marriages."

The court is expected to hear the history of the breakaway Mormon sects in the next few days, when Texas Ranger Nick Hanna testifies.

Hanna was one of the officers who raided the FLDS Yearning for Zion Ranch in Eldorado after Blackmore and his wife were accused of taking a 13-year-old across the U.S. border in 2004.

Thousands of pages of marriage records were seized during the investigation that led to the arrest of Jeffs, 61, who is now serving a life sentence for child sexual assault.

Texas Ranger Nick Hanna heads into a B.C. courtroom in Cranbrook B.C. for the trial of Winston Blackmore and James Oler, accused polygamists. (Bob Keating/CBC)

But the Canadian case against Blackmore and others became mired in legalities because of a lack of clarity around polygamy laws.

Several efforts to clarify legislation followed, taking the case to the B.C. Supreme Court level.

In 2007, then-attorney general Wally Oppal appointed special prosecutor Richard Peck to review RCMP files, but he agreed with previous opinions that the law may not be constitutional.

Eventually, after two more special prosecutors were appointed, charges were laid in 2009, then stayed.

Where is the line?

Then in 2011, the B.C. Supreme Court ruled that laws banning polygamy were constitutional and did not violate the religious freedoms guaranteed in the Charter of Rights and Freedoms.

That cleared the way for the Blackmore/Oler trial to go ahead today.

This week in Cranbrook B.C. Supreme Court Justice Sheri Ann Donegan will hear arguments and eventually make a decision that could sketch out new limits for religious freedom in Canada.

Accused polygamist Winston Blakcmore heads into court in Cranbrook B.C. (Bob Keating/CBC)

Blackmore and Oler are expected to argue that having multiple wives is their religious right, and brings them closer to God.

The Crown argues polygamy is a clear violation of the Criminal Code, and leads to the subjugation of women and children.

None of the allegations have been proven in court and the case is being heard by judge alone.

Mothers and daughters enjoy a ride in a sled in snowy Bountiful B.C. (CBC)