A Boston federal magistrate judge has ruled that Amphastar Pharmaceuticals Inc. must pay opponent Momenta Pharmaceuticals Inc.’s legal fees in a dispute over Amphastar’s failure to produce court-ordered documents.

However, U.S. District Magistrate Judge Robert Collings stopped short of non-monetary sanctions. Although Amphastar’s violations “were quite serious and possibly contumacious,” he said, they did not require case-related sanctions such as a ruling for the plaintiffs on a substantive issue.