Charleston City Council could face a potentially significant property rights battle Tuesday when members debate an ordinance requiring landowners be compensated when their property is downzoned.

The idea for a “government-initiated downzoning ordinance” was offered by City Councilman Aubrey Alexander. It would require that assessments of lost value be done when a zoning category changes and that landowners be compensated.

“My position is there is value and when you take a value of anything from anybody, then the right thing to do is to compensate them,” he said. The proposal is supported by some in the realty industry.

But the idea has been assailed as “radical” by local preservationists, while Mayor Joe Riley said the burden would become immeasurable if such changes had to be evaluated for cost for everyone involved.

“The huge financial expense to the city posed by the bill cannot be overstated,” Riley said in a letter asking council to kill the measure outright. ”Most rezonings affect value, at least to some degree.”

Additionally, Riley said any degree of land-use planning or citizen-requested zoning initiatives would come to a halt if the potential cost impact had to be absorbed by the city.

“Meaningful planning and zoning are the heart of a thriving, dynamic community,” Riley said. “This bill will severely undercut both.”

Alexander said the ordinance is being proposed to compensate those on the losing end when the city decides to alter the property rights.

He did not have a forecast of what it would cost, but that number would potentially go into the millions of dollars, when such areas as future use, landscaping and building condition get evaluated.

Part of the bill stems from what Alexander said was an outcry when a large portion of the Cannonborough-Elliottborough neighborhood was downzoned in what he said was a move by the city to curtail the expanse of night spots.

The ordinance sets up an appraisal procedure for those slighted, he said. “It gives David a rock to defend himself against Goliath,” he said.

“If the community is willing to take someone’s property, what are they willing to pay?” he added.

One of the chief opponents is the Preservation Society of Charleston, which said protection of Charleston historic buildings, height restrictions and protecting both neighborhoods and commercial districts are all products of city regulations.

“If the proposed ordinance were to pass, the city would be bankrupted if it sought to make changes to current regulations,” the society said in a message asking supporters to come out against the idea.

Additionally, the city would lose the ability to protect residents and businesses from changing conditions “that might otherwise lead to inappropriate intensification of commercial uses, overscaled new construction, inappropriate development density, destructive alterations to historic properties and any other future negative impacts that we can’t possibly predict today.”