(Reuters) - Pennsylvania attorney disciplinary officials have dropped their appeal of an injunction that bars them from implementing an anti-discrimination rule governing lawyers' conduct in the state.

The Pennsylvania Supreme Court's disciplinary board and its prosecutorial arm, the Office of Disciplinary Counsel, notified the 3rd U.S. Circuit Court of Appeals on Tuesday that they're dismissing their appeal. A federal judge ruled late last year that the rule violated the First Amendment.

The Hamilton Lincoln Law Institute, which challenged the constitutionality of Pennsylvania Rule 8.4(g) on behalf of plaintiff Zachary Greenberg, heralded the withdrawn appeal as a victory for free speech.

HLLI founder Theodore Frank said the state's retreat and the standing injunction will serve as ammunition for other attorneys who are opposing the adoption of the American Bar Association's Model Rule of Professional Conduct 8.4(g), upon which the Pennsylvania rule is based, in their own states.

"The ABA has been pushing this rule for a few years. There are battles in states over whether to adopt it," Frank said. "This is the first federal judicial decision over the constitutionality of this rule."

The decision by Pennsylvania officials to dismiss their appeal came two days before their appellate brief was due.

The model ABA rule prohibited a lawyer from "engag(ing) in conduct that the lawyer knows or reasonably should know is harassment or discrimination on the basis of race, sex, religion, national origin, ethnicity, disability, age, sexual orientation, gender identity, marital status or socioeconomic status in conduct related to the practice of law."

Greenberg, a First Amendment attorney with the nonprofit Foundation for Individual Rights in Education, argued that he was at risk of violating the new rule, as he gives presentations about First Amendment cases that include offensive and derogatory language.

A federal judge agreed, finding in December that the rule "will hang over Pennsylvania attorneys like the sword of Damocles," and imposed a preliminary injunction that blocked the rule's implementation.

The rule "promotes a government-favored, viewpoint monologue and creates a pathway for its handpicked arbiters to determine, without any concrete standards, who and what offends," U.S. District Judge Chad Kenney held.

A spokeswoman for the Administrative Office of Pennsylvania Courts, which represented the state officials in the case, did not respond to a request for comment.

The case is Greenberg v. Haggerty, et al, 3rd Circuit Court of Appeals, No. 20-3602.

For Greenberg: Adam Schulman and Theodore Frank of Hamilton Lincoln Law Institute

For defendants: Michael Daley and Megan Linsley Davis of Administrative Office of Pennsylvania Courts