WASHINGTON — The Supreme Court appeared divided on Monday over the constitutionality of a procedure that makes it easier to challenge questionable patents.

The procedure, created by Congress in 2011, resembles a trial in federal court but is conducted by an executive-branch agency. Supporters say it helps combat “patent trolls,” or companies that obtain patents not to use them but to demand royalties and sue for damages. Opponents say the procedure violates the Constitution by usurping the role of the federal courts, violating the separation of powers and denying patent holders the right to a jury trial.

The case grew out of a dispute between Oil States Energy Services, which owned a patent for protecting wellhead equipment during hydraulic fracturing of oil wells. A competitor, Greene’s Energy Group, successfully challenged the patent under the procedure, called “inter partes” review, which is Latin for “between the parties.”

An administrative tribunal created by the 2011 law, the Patent Trial and Appeal Board, ruled that the patent was invalid. According to a brief filed by the federal government, the tribunal had, as of July, canceled all or part of more than 1,300 patents.