A Boston-based attorney may testify as Northrop Grumman Corp.'s expert witness in a lawsuit accusing the company of improperly charging workers retirement plan fees, a federal court said.

Disqualifying Marcia Wagner as an expert wasn’t necessary because the plaintiffs didn’t show that her legal partner, who previously worked on another matter for the plaintiffs, shared confidential information with Wagner, said Judge Andre Birotte Jr. of the U.S. District Court for the Central District of California.

Evidence showed that the legal partner, who works at Wagner’s firm in the St. Louis office, is properly screened from any participation in the case,...