The company had 30 days to stop the leak it caused by not following its submitted plans.
The pipeline company breached a groundwater aquifer, causing water to flow uncontrolled into a trench.
The senator was quickly ushered away from the scene.
A group of demonstrators remained on the grounds after the event permit expired.
That includes at least one fluid release into wetlands, which is a violation.
The ongoing drought has led to worryingly low stream flow levels in some areas.
The spill happened July 6 during a drilling procedure.
Officials used rotor downwash in an attempt to clear Line 3 protesters.
People from Minnesota and out of state were among those arrested last week.
Construction on the Minnesota portion of the pipeline began in December.
It happened in Hubbard County, northwestern Minnesota.
The protests in Carlton County are just the latest in demonstrations against the project.
Construction on the pipeline started earlier this month.
The project has attracted criticism from environmental and tribal groups.
"We cannot continue to legitimize and provide cover for the MPCA's war on black and brown people," their resignation letter states.
The Enbridge pipeline replacement project would replace a crude oil pipeline in northern Minnesota.
The move came as the legislature began its fourth special session.
The Supreme Court declined to take up a challenge against the project.
It's a setback for pipeline company Enbridge.