A white fifth-grade teacher at a private school in tony Bronxville is accused to holding a mock slave auction in which black students were put in “imaginary chains” while their white classmates were urged to bid on them — as she played auctioneer.

Vernex Harding, the mom of one of three black students in the social-studies class at The Chapel School in Westchester County, said her child told her that the teacher took him and the other two kids, both girls, into the hallway earlier this week and “started to put imaginary chains on our necks, our wrists and shackles on our ankles.”

“I was in shock,” Harding told The Post on Friday.

The black students were then brought back into the classroom, where the white kids were pushed to bid on them while teacher Rebecca Antinozzi acted as the auctioneer, the mom said.

“When they got inside the classroom, she started a bidding process going, ‘$100, $200 …’ and said to one of the other kids, ‘You’re a wealthy white man’ and started bidding at $300,” Harding said.

The alleged incident happened Tuesday at the pre-K through-eighth-grade school, where annual tuition runs up to $14,000.

“He was humiliated,” Harding said of her child. “My son doesn’t want to see her again, and I don’t want to see her again.”

New York Attorney General Letitia James confirmed to The Post on Friday that she has launched a probe into the matter.

“The reports of racist ‘lessons’ by a teacher at The Chapel School are deeply troubling,” James said in a statement. “My office is monitoring this matter closely.”

A source familiar with the situation said James’s office has been contacted by parents of children at the school –- both black and white –- who went home feeling “very uncomfortable” by the incident.

The parents complained to James’s office that there has been previous incidents involving teachers and black students that “bordered” on being racist, “but nothing as egregious as this,” the source said.

Antinozzi’s lawyer, Jordan Brooks, said in a statement: “The portrayal of the history lesson that has been reported is inaccurate, out of context, contains false facts and ignores the overwhelming support of Ms. Antinozzi from dozens of parents at the school, including several letters of support from African-American parents with children who have been taught by Ms. Antinozzi.

“Ms. Antinozzi loves her students and is beloved by them. To the extent anyone took offense to a small portion of the overall lesson that day that was used solely to emphasize the tragic injustice of slavery, it certainly was never intended,” Brooks said.

The Chapel School did not return a request for comment by The Post, but its principal called the lesson “racially insensitive and hurtful” in an e-mail, according to PIX11.

The teacher has since been removed from the classroom, the news outlet reported.

Meanwhile, a parent of two students who did not want to be identified told The Post that Antinozzi is “a great teacher” who “cares about every child.”

“If it happened as I read it, it’s a horrible error in judgement, but it does not represent who she is and what she means to the kids there,” the parent said.