With the threat that their kids won’t be allowed to attend school, more than 150 Rochester families have scrambled in the past week to comply with a Minnesota law that requires students to be vaccinated unless they receive an official exemption.

School district officials took the unusual step of issuing the ultimatum last week because 204 students had not complied with the law that requires all students enrolled in grades kindergarten to grade 12 be immunized or officially exempted.

They told families they had until March 1 to meet the requirement or their children would not be allowed to attend classes.

Superintendent Michael Muñoz said it was the first time in his six-year tenure that the district had taken such an action.

By the time school began Wednesday, 80 students who still hadn’t complied weren’t allowed to attend class. Instead, school officials notified their families, guardians or emergency contacts about the situation.

At the end of the day, 68 students still hadn’t met the state immunization requirements. Rochester, the seventh-largest school district in Minnesota, has more than 17,600 students.

A woman who answered the phone at the Olmsted County immunization clinic reported that an unusually high number of people have come in for vaccinations in the past week.

In the past seven days, 117 students have proved they were vaccinated, while 19 filed exemptions, school officials said.

Students can be exempted if there is a medical reason or if the parent or guardian provides a notarized statement saying it’s a violation of their “conscientiously held beliefs.”

Minnesota is one of 18 states that allow exemptions for philosophical or personal beliefs.

Rochester school officials have said repeatedly that they don’t know why so many students hadn’t provided proof they were vaccinated or filed exemptions six months into the school year.

They pointed out the students were spread throughout the district and grades.

Minnesota schools must submit an immunization report to the state Department of Health by Dec. 1 unless they request a 60-day extension.

Rochester school officials said they had worked “diligently” since January to inform families that students must be vaccinated to attend school, or provide documentation for an exemption.

In a written statement, district officials said they took “every reasonable measure” to prevent students from missing school.

“It was the district’s sincere hope that all parents would comply with the law and avoid having their children miss any school,” the statement said.