Campaigners are increasing efforts to have police officers removed from schools in Greater Manchester.

Teaching unions and academics have said plans to bolster the police presence in schools in the region will disproportionately and unfairly affect students from minority backgrounds and those living in areas of deprivation.

Billboards went up across the city and a petition reached more than 1,300 signatures in opposition to plans by the Greater Manchester Combined Authority (GMCA) to put a further 20 police officers in schools across the region.

In March the Guardian revealed that more than 650 police officers were working in schools in the UK, with many assigned to sites in areas of high deprivation.

The activities of school police officers, often known as safer schools officers (SSOs), range from being a point of contact for teachers to more intensive interventions such as stop and search and surveillance of children suspected of being gang members.

While police forces say SSOs play an important role in keeping children safe, campaigners and charities say their presence risks criminalising young people, could exacerbate inequalities, and creates a culture of low expectations and a climate of hostility.

Remi Joseph-Salisbury, a presidential fellow in ethnicities and inequalities at the University of Manchester, said schools should not be a place with a hostile climate or where students worry about being criminalised.

“Police presence is not conducive to student wellbeing or to good learning, police don’t belong in schools,” he said.

Joseph-Salisbury is one of more than 300 academics and community workers, including the community interest company Kids of Colour, who have previously signed an open letter asking Andy Burnham, the mayor of Greater Manchester, to keep police out of schools in the area.

Laura Connelly, a lecturer in criminology at the University of Salford, and one of the authors of the Decriminalise the Classroom report, said communities have grave concerns about police in schools.

“Young people, parents, teachers and community members are concerned that police in schools will replicate the same race and class inequalities we see in policing in our communities,” she said.

She said minor disciplinary issues risked being escalated into criminal matters, “lumbering young people with criminal records” that would shape their future.

“If the GMCA is really committed to keeping young people safe, it will invest in the community infrastructure, mental health support, youth workers and teachers that are so desperately needed. Young people need support not suspicion.”

In a video for the campaign, a student, Evelyn, said police in schools caused heightened anxiety among students. “If something happens, like if there is a fight, a school with police in those children could be criminalised and then that stays on their record and then you can’t change it,” she added.

Bev Hughes, the deputy mayor of Greater Manchester for policing, crime and criminal justice, said the GMCA was committed to the initiative and police would be assigned to schools only if a headteacher requested extra support.

“We want any police presence in schools to help build positive relationships between young people and the police,” she said. “Not only can this help to promote awareness of the risks of violent or antisocial behaviour amongst young people, it can also support individual youngsters who are vulnerable.”