The legacy of late Supreme Court Justice Antonin Scalia's includes numerous pro-business decisions, and his death creates considerable uncertainty for employers.

Justice Scalia's passing is “really bad news for employers,” said Richard R. Meneghello, a partner at Fisher & Phillips L.L.P. in Portland, Oregon.

He was a leading voice on conservative issues favorable to employers, and though much of Supreme Court deliberations are secret, “we've got to assume the charisma that was on display in the public all the time was also very influential when he was sitting around talking with the other justices at conference,” Mr. Meneghello said.

“He has written numerous rulings that create the rules of the road, so to speak,” in the workplace, said Gerald L. Maatman Jr., a partner at Seyfarth Shaw L.L.P. in Chicago.

Justice Scalia's pro-employer opinions include the court's 2011 ruling in Wal-Mart Stores Inc. vs. Betty Dukes et al., which shattered a proposed gender discrimination class of 1.5 million, resulting in smaller groups of plaintiffs.

“If you're an employer, that's probably the most important decision involving class action laws in the workplace,” said Mr. Maatman. “It had a huge impact on employers in terms of changing the playing field and cutting back on the number of class actions that can be certified for employment discrimination.”

“The biggest single impact I would say he has had is in the arbitration area,” said Charles A. Sullivan, a professor at Seton Hall University School of Law in Newark, New Jersey. “He's been a leading figure in jurisprudence about arbitration being enforceable.”

Justice Scalia's majority opinion in AT&T Mobility L.L.C. vs. Vincent and Liza Concepcion in 2011 held that arbitration agreements may contain a class action waiver, while his majority opinion in American Express Co. et al. v. Italian Colors Restaurant et al. held in 2013 that class action waivers in arbitration agreements are enforceable.

Justice Scalia also wrote the court's 2010 majority opinion in Robert Morrison et al. v. National Australia Bank Ltd., which held that foreign investors who bought non-U.S. based companies' stock on foreign exchanges cannot sue in the United States.

However, Justice Scalia wrote the dissenting opinion in David King et al. v. Burwell. The June 2015 ruling, which employers welcomed, upheld 2012 IRS rules that have enabled millions of uninsured people to use federal premium subsidies to buy health insurance in the federal exchange as well as state exchanges.

And he wrote the June 2015 majority opinion in EEOC v. Abercrombie & Fitch Stores Inc., which said employers must consider whether a job applicant needs an accommodation based on religious needs, even if the applicant does not mention the subject.

The opinion shows that when Justice Scalia did agree with the court's liberal wing, those justices “wanted to use it,” said Mark I. Schickman, a partner at Freeland Cooper & Foreman L.L.P. in San Francisco.