The ban, which took effect July 1, prohibits products derived from force-fed birds. Foie gras is made from goose or duck livers that were enlarged by force-feeding ducks through funnel-like tubes.
A Canadian exporter of the fattened duck liver delicacy, a foie gras producer based in New York and a Southern California restaurateur claim the law isn't specific enough.
The plaintiffs said there is nothing in the law to measure when a bird has been fed "too much." They said the law violates the federal constitution's commerce clause.
The lawsuit seeks first a temporary, then permanent barring of the ban's enforcement.
The Associated Press contributed to this report.