Sidney Dickstein, a founding partner of one of Washington’s largest law firms, Dickstein Shapiro LLP, and whose clients included blacklisted filmmakers during the McCarthy era and a publisher charged with obscenity violations, died May 17 at a hospital in Baltimore. He was 89.

The cause was interstitial lung disease, said a daughter, Ellen Kominers.

Mr. Dickstein, a Bethesda resident, began his legal career in the 1950s representing labor unions and defending alleged Communists and Communist Party sympathizers during the investigations of Sen. Joseph R. McCarthy (R-Wis.).

Mr. Dickstein and a law partner, David I. Shapiro, founded a firm in New York City in 1953 and moved the headquarters to Washington three years later.

The firm, which grew to include more than 250 lawyers across the United States, developed specialties in First Amendment rights, labor and antitrust cases and class-action lawsuits. Shapiro died in 2009.

Sidney Dickstein died May 17 at 89. (Photo by Freed Photography/Courtesy of Dickstein Shapiro LLC)

Mr. Dickstein helped represent Hollywood figures involved in the making of “Salt of the Earth” (1954), a film about striking Mexican American miners that initially was condemned as Communist propaganda and was denied widespread distribution. The film later became a cult classic.

“If it is communistic to depict poverty in the United States, then Life magazine, the New York Times and President Johnson himself, in trying to open our eyes on this subject, are purveyors of Communism,” Mr. Dickstein argued in court, according to thebook “Salt of the Earth: The Story of a Film” by director Herbert Biberman.

The lawsuit, which alleged a conspiracy to suppress the movie, was ultimately dismissed by a federal court.

Mr. Dickstein appeared several times before the U.S. Supreme Court, including in the 1960s as an attorney for Ralph Ginzburg, the publisher of Eros, an erotic magazine. The matter involved Ginzburg’s allegedly salacious promotion of his publications and was one of the last major federal obscenity cases heard by the high court.

The court upheld the conviction of Ginzburg, who served eight months in prison. The decision was sharply criticized by free-speech advocates and is regarded as significant in the history of First Amendment law.

In the 1970s, Mr. Dickstein helped represent Watergate figure Charles W. Colson, a top aide to President Richard M. Nixon, in connection with a break-in at the office of the psychiatrist of Daniel Ellsberg, who angered the Nixon administration by leaking the Pentagon Papers, a secret history of the Vietnam War.

Sidney Dickstein was born May 13, 1925, in Brooklyn. He was a 1947 government graduate of Franklin and Marshall College in Lancaster, Pa., and received a law degree from New York City’s Columbia University in 1949.

Mr. Dickstein remained senior counsel at his law firm until his death. He was credited with establishing the firm’s partnership with the Duke Ellington School of the Arts, a D.C. high school that specializes in the performing and visual arts.

In 2000, he published a memoir, “Adventures in the Law, 1947-2000.” He was a past president of the Washington chapter of the American Jewish Committee.

His wife of 60 years, Barbara Duke Dickstein, died in 2013. Survivors include three children, Ellen Kominers of Bethesda, Nancy Stern of Jacksonville, Fla., and Matthew Dickstein of Fort Collins, Colo.; and five grandchildren.