TO ITS CRITICS, the list of Wal-Mart's corporate sins could fill one of the retail chain's giant "supercenters." Wal-Mart, popular among bargain hunters for everything from toasters to tires, is criticized, particularly by unions, for paying low wages and providing paltry health benefits to its nonunionized employees. This week a judge certified class action status in a sexual discrimination lawsuit against the corporation. Independent stores dislike the chain for its ability to price them out of the market. But dislike of Wal-Mart's corporate practices shouldn't be the basis for zoning laws aimed at keeping Wal-Mart's combined retail and grocery supercenters out of the region.

That's precisely what Montgomery County Executive Douglas M. Duncan wants to do. With the support of Giant, Safeway and local supermarket unions, Mr. Duncan is asking the county council to toughen zoning rules for stores larger than 120,000 square feet that devote at least 10 percent of their floor space to groceries. It's not a coincidence that this narrow definition covers huge nonunionized grocery-selling stores such as Wal-Mart's supercenters, SuperTarget and Wegmans, all potential competitors with the unionized Giant and Safeway supermarkets, which fall under the 120,000-square-foot limit. Nor is it a fluke that the proposal exempts club membership stores such as union-friendly Costco and non-grocery outlets such as Home Depot.

Mr. Duncan's proposal is based on the absurd contention that grocery-selling big-box stores that don't require a membership card generate far more traffic than their counterparts. That idea was rightly questioned by a few members of the Montgomery County Council and criticized by the county's planning department, which found no evidence that these stores tie up roads more than other big boxes. Zoning rules already mandate a sharp look at environmental and traffic impacts before construction of a new commercial building; decisions can be appealed to the Board of Appeals, which holds public hearings.

Concern about the effect of big new stores on surrounding communities is legitimate, but local planning decisions should be based on sound, uniform principles, not on arbitrary criteria targeting specific disfavored companies. Indeed, employees who alleged that Wal-Mart paid women less and granted them fewer promotions are successfully raising their issues through their class action lawsuit -- not through manipulating local zoning laws that have nothing to do with employment law. If there is concern over Wal-Mart's labor practices, its employees have the right to unionize; if there is concern over stingy health care packages, workers should target that issue directly. County government should not misuse its considerable planning powers to punish certain companies or reward others.