Federal court proceedings throughout New Jersey were abruptly canceled on Monday because of uncertainty over whether Alina Habba had the authority to serve as acting U.S. attorney — a title she was given last week as her interim appointment as the state’s top federal prosecutor was about to expire.

Pretrial conferences and hearings set for defendants to enter pleas were called off, according to four lawyers who received word that their clients’ scheduled court appearances had been canceled. A grand jury that was expected to meet to consider indicting defendants on new criminal charges was put on hold. And a drug trial that was set to start Aug. 4 in Camden, N.J., was moved to Pennsylvania after a lawyer representing one of the defendants filed a motion arguing that Ms. Habba’s prosecutorial authority was unconstitutional.

“I’ve never seen anything like this,” said Maria Noto, a former president of the Association of Criminal Defense Lawyers of New Jersey. “We’re all incredulous.”

Ms. Noto said she was notified on Monday that a judge had canceled a hearing for a client who expected to enter a guilty plea later this week.