Arguments are underway before the Supreme Court of Canada in a long-awaited case over the federal Impact Assessment Act.
The court is expected to hear from legal experts and environmental groups that support the law.
Nine of 10 provinces, led by Alberta, argue that the law intrudes on provincial jurisdiction.
Alberta is particularly concerned about the effect the law might have on its ability to export its oil through pipelines.
Last May, the Alberta Appeal Court ruled the law was outside federal jurisdiction.
This week’s hearings are an appeal of that decision.