A Nassau County jail inmate pleaded not guilty to felony assault charges Thursday after authorities accused him of punching a correction officer last month and knocking him unconscious.

Angel Hernandez, 22, of Uniondale, also injured two other correction officers who stepped in to try to control him after the “unprovoked” attack, a prosecutor alleged in court.

Hernandez already is jailed on other offenses he’s denied committing, which court records show include attempted murder and weapon charges.

More than two dozen Nassau correction officers rose from their seats during the inmate’s Hempstead court arraignment Thursday.

Correction union leader Brian Sullivan said it was a show of solidarity for a veteran colleague “with a spotless record” who suffered a concussion and other injuries that have left him unable to work since the Aug. 22 encounter.

Felony complaints charging Hernandez with three counts of second-degree assault allege he shouted to another inmate in a jail visiting room, was told to stop, and was taken from the area after he ignored the order. They allege Hernandez then swung at the correction officer, hitting him in the back of the head.

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But Hernandez’s attorney, Nicholas Marino, told District Court Judge Darlene Harris his understanding was his client got into an altercation with another inmate and correction officers got hurt trying to break it up.

The judge set Hernandez’s bail at $200,000 cash or $300,000 bond, which is separate from his $500,000 bail, cash or bond, in the attempted murder case.

The violence in the jail’s visiting area broke out at a time when the East Meadow facility’s safety and security has been questioned, including during a summer rally by correction union members.

On Sept. 4, nine correction officers needed hospital treatment for minor injuries after inmate violence erupted in a jail dorm.

“To be clear, this incident actually occurred in a fully staffed area of our facility,” Sullivan said of the Aug. 22 event. “That shows you the problems we have when there’s cuts in other areas of the facility, when something like this can happen in a fully staffed area.”

Nassau County Sheriff Michael Sposato has defended the safety of the jail, previously discounting union member complaints as the grumblings of employees who wanted to do fewer patrols.

“We have a zero tolerance policy as it relates to acts of violence,” Sposato said Thursday in a statement. “We will make every effort to ensure that anyone committing such acts of violence will be arrested, charged and prosecuted to the fullest extent of the law.”