Ms. Calvert said that the fact that adoptive parents receive the same amount of paid leave as biological mothers supported the plaintiffs’ argument that the leave was for bonding, but that this fact was not decisive.

A policy like Jones Day’s does not appear to have been tested in court, but in 2015 CNN settled an analogous case with a biological father.

David Lopez, a former general counsel of the Equal Employment Opportunity Commission, said Mr. Savignac appeared to have a strong claim that his firing was unlawful. Mr. Savignac was fired three business days after he and Ms. Sheketoff said in an email to the firm that the leave policy was discriminatory, and he had previously earned strong performance reviews, according to the complaint.

Jones Day defended its policy, saying it grants birth mothers eight weeks of paid disability leave to avoid having to ask for medical evidence that they are still recovering from childbirth. The firm said the firing of Mr. Savignac had not been in retaliation for criticizing the leave policy, which it said he and Ms. Sheketoff had done in 2018 without repercussions. Rather, it said, it fired him because he had shown a “lack of courtesy” to colleagues and an “open hostility to the firm,” citing his email.

The firm also said its adoption-leave policy reflected the unique demands that adoptive parents can face, like foreign travel and legal proceedings.

Jones Day’s policy is at odds with a trend in which companies are increasingly eliminating the distinction between fathers and mothers or primary and secondary caregivers. They award all employees the same amount of family leave for a new child, though women who give birth can sometimes receive additional time to recover through disability leave.