Detroit woman Rebecca Bredow was told by a judge that she had until Wednesday for her son to be up-to-date with all vaccinations.
But as The Washington Post reports, Ms Bredow refused to do so, and she was sentenced for contempt of court for ignoring the order.
Ms Bredow had argued her religious beliefs led her to refuse the vaccinations.
"I am an educated vaccine-choice mother,” she said in court.
“I would rather sit behind bars standing up for what I believe in, than giving in to something I strongly don't believe in.”
Parents in the state of Michigan are allowed to skip or delay vaccinations due to personal beliefs, the BBC reports.
However, the mother faced legal repercussions because she had reneged on her initial agreement with her ex-husband from 2016 about having their son vaccinated.
During sentencing, Judge Karen McDonald told Ms Bredow: “I understand you love your children. But what I don’t think you understand is that your son has two parents, and dad gets a say.”
The judge also insisted that the 9-year-old be vaccinated.
This article originally appeared on marie claire.