At issue is whether the Minnesota Public Utilities Commission should grant a certificate of need for replacing the 1960s-era pipeline, which carries Canadian crude from Alberta across Minnesota to Wisconsin.
Tribal and environmental groups plan to rally against Line 3 at the Capitol at 4 p.m. Thursday, then march to the 6 p.m. hearing at a St. Paul hotel.
The Commerce Department says Enbridge has failed to establish the need for the project.
But Enbridge says Line 3 is a critical piece of its network. Supporters turned out heavily at Tuesday’s first hearing in Thief River Falls.
The PUC plans to decide in April.