According to BBC, an online petition has been set up and a pan-African women's organisation is mobilising to get the president to apologise and reverse his comments.
Mr Magufuli warned schoolgirls at a rally on Monday that: "After getting pregnant, you are done."
Mr Magufuli, who was speaking at a public rally in Chalinze town, said that young mothers would be distracted if they were allowed back in school:
"After calculating some few mathematics, she'd be asking the teacher in the classroom: 'Let me go out and breastfeed my crying baby.'"
He said that men who impregnate the schoolgirls should be imprisoned for 30 years and "put the energy they used to impregnate the girl into farming while in jail," He was quoted.
The online petition says that the president's support for the expulsion law would end the education of many girls and "propagate more discrimination".
It instead calls for the girls to be protected from early pregnancies while in school.
A law passed in 2002 allows for the expulsion of pregnant schoolgirls.
The law says the girls can be expelled and excluded from school for "offences against morality" and "wedlock". BBC reports.
Women's rights groups have recently been urging the government to change the law.