The executive director of the Port Authority of New York and New Jersey and three others were subpoenaed Tuesday by a New Jersey legislative committee investigating the George Washington Bridge lane closing affair.

The subpoenas were issued to Port Authority boss Pat Foye, Christie administration chief spokesman Michael Drewniak, former Christie staffer Christina Renna and Port Authority Commissioner William (Pat) Schuber, the Star-Ledger of Newark reported.

The four are required to appear before the committee in Trenton in early May to offer testimony on the lane diversions. Committee Co-Chairman John Wisniewski, a Democrat, has said as many as 10 people may be ordered to testify.

On Monday, Republican Gov. Chris Christie would not say whether he expected to called to testify himself or whether he would comply.

The latest subpoenas follow more than two dozen already issued this year for documents related to the September 2013 lane diversions that snarled traffic in Fort Lee, N.J.

“With these subpoenas for testimony, the joint committee is moving to a key stage of its investigation into how this abuse of government power and threat to public safety occurred,” Wisniewski and his Democratic co-chair, Senate Majority Leader Loretta Weinberg, said in a statement.

The panel already has issued a number of subpoenas for documents and other information related to the investigation of suggestions that top Christie appointees orchestrated traffic jams around the nation’s busiest bridge in Fort Lee last year as part of an alleged political payback scheme.

Wisniewski said investigators still only have a partial picture of what happened in the period before access lanes to the bridge were deliberately closed over a four-day period last September.

The most sensational piece of evidence unearthed so far is an email from Kelly to David Wildstein, a Port Authority executive that read: “Time for some traffic problems in Fort Lee.”

Wildstein replied: “Got it.”

Wisniewski told CNN that investigators “still don’t know what happened before that email,” which was sent weeks before the lane closures occurred.