The case was brought by the Preservation Society of Charleston and the South Carolina Coastal Conservation League who sued the U.S. Army Corps of Engineers saying they should have considered the terminal's impact on the city's historic district before approving the project.
In an order signed Wednesday, U.S. District Judge Richard Gergel agreed that the State Ports Authority could intervene in the case on the side of the corps.
Both plaintiffs have agreed the Ports Authority could participate. But they said they were not agreeing with the authority's position on the terminal.
In asking to intervene, the Ports Authority said that the outcome of the case could affect its ability to renovate an old warehouse on the Cooper River waterfront as a new passenger terminal.
Attorneys also noted the authority is a state agency and the outcome of the case could affect its ability to facilitate commerce in the state.
Last week Gergel signed a scheduling order setting a November trial date.
When the project was originally announced, the State Ports Authority had hoped the new terminal could be open by last year. But the project has been slowed by both state and federal lawsuits and a challenge to a permit issued in December by state regulators.
The case Gergel is hearing was brought in Washington, D.