President Obama’s decision to issue recent recess appointments is constitutional, because recent pro forma sessions of the U.S. Senate — some lasting just a few seconds — didn’t constitute legitimate sessions that could block such appointments, the Justice Department said in a memo released Thursday.

Congressional Republicans have assailed Obama’s decision to issue recess appointments last week of Richard Cordray to lead the new Consumer Financial Protection Bureau and of three nominees to serve on the National Labor Relations Board. Several GOP lawmakers criticized the move as disregarding the history and legality of Senate procedure.

In a 23-page memo dated Jan. 6, Virginia A. Seitz, the assistant attorney general for the Office of Legal Counsel, wrote that although the Senate held pro forma sessions from Jan. 3 to Jan. 23, “those sessions do not interrupt the intrasession recess in a manner that would preclude the President from determining that the Senate remains unavailable throughout to ‘receive communications from the President or participate as a body in making appointments.’ ”

The memo, drafted at the request of the White House, was not released until Thursday because Office of Legal Council opinions are released after a stringent review by Justice officials.

Sen. Charles E. Grassley (Iowa), the ranking Republican on the Senate Judiciary Committee and a leading GOP critic of Obama’s decision, said the opinion altered the separation of powers as described in the Constitution.

The opinion “relies on no Supreme Court decision and many conclusions are unsupported in law or the Constitution,” Grassley said in a statement. He added later that the opinion “flies in the face of more than 90 years of historical practice.”

But the opinion could dampen potential legal challenges to Cordray’s appointment by outside groups. In a speech Thursday, U.S. Chamber of Commerce President Thomas J. Donohue called the recess appointment “deeply disappointing.” The Chamber previously “condemned” the move.

Later, in an interview with Fox Business, Donohue backed away from any legal challenge.

“I’m sure the Department of Justice gave it a very fair look,” he said. “I think there’ll be lawsuits. I’m not sure we’re going to take them.”

During a news conference Thursday, Cordray said he spoke with Donohue on Wednesday and was in “frequent” communication with the chamber. Cordray, the former Ohio attorney general, said he has been a member of his local chamber of commerce for 20 years and had represented the group as a lawyer. He said the CFPB could be a boon for law-abiding businesses.

“They should embrace the bureau,” he said. “We are going to support the honest and responsible businesses in the marketplace.”