The city of Roswell and a Smyrna-based billboard company appear to be heading to court over an advertisement facing Ga. 400.

Clear Channel Outdoor had city permission to switch the billboard from a mechanical style, with reversable panels, to an electronic display. But when the company earlier this month changed the structural support for the sign, the city contended it had substantially changed the billboard, and violated the permit.

In a letter sent to company president Chris Russell, the city ordered the sign taken down by 5 p.m. Dec. 23.

The billboard violates current zoning practice in Roswell, but had been grandfathered-in because it was installed in 2000.

In an e-mail Tuesday, responding to a request for comment, Russell said the company will protect its rights in court. “We are disappointed in the action taken by the city because we had all necessary approvals and permits in place,” Russell wrote. “Unfortunately, we will have to look to the courts for relief from this action taken by the city of Roswell.”

City Attorney David Davidson said the company did not have authority to take down the support system and put up a new sign. “They did have permits, but they went beyond the scope of their permit.”