The case centres on whether patients can grow their own pot for medicinal purposes.
Last April new federal marijuana laws banned all home growing for medical purposes, meaning users would have to buy pot from licensed growers.
But four patients who grow their own marijuana challenged the new regulations in court, arguing licensed producers will inflate the price, making medical marijuana too costly.
Last March, just before the home growing ban took effect, lawyers won a temporary injunction allowing patients to continue cultivating their own marijuana, until the case is finally decided.
In December the federal government lost an appeal to strike down that injunction. The new hearing is expected to run for 15 days.
Other challenges underway
The federal government's new regulations are also facing a legal challenges from at least one company that failed to get licensed under the new program.
Since the new rules came in, at least 15 operations have been licensed to sell medical cannabis.
At least 13,000 patients have registered with the new licensed producers. Prices range from as low as $2.50 a gram to as high as $15, though most are between $8 and $10.
Health Canada says it does not know how many patients continue to grow their own marijuana because of the injunction.
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