Campbelltown MP Greg Warren and local parents are concerned a new policy aimed at cracking down on out of area enrollments at schools could separate siblings.
Mr Warren said parents could be forced to send their children to different schools following the announcement of a new state government policy.
He said the policy change had also left opposition spokeswoman for education Prue Car and Rosemeadow Public School P&C president Tammy Scowcroft fuming.
"It's clear this Liberal government is more focused on causing parents and students unnecessary stress, rather than focusing on building strong vibrant school communities," he said.
"Many schools in Campbelltown are falling apart and still aren't fully air-conditioned - the government should address those issues first.
"This policy shows just how out of touch the Liberals are with communities in Western Sydney like Campbelltown."
The changes outlined by the Department of Education state "like other non-local students, siblings may not be enrolled at a school [that] has reached its cap or local enrolment buffer".
Caps are determined by the number of permanent classrooms - posing a major problem for schools like Rosemeadow Public School that have a significant number of demountable classrooms.
Almost one third of classrooms at Rosemeadow Public School are demountables.
Ms Snowcroft said the policy was "not good at all".
"Our parents are absolutely horrified," she said.
"We have a huge number of parents that have children with issues - particularly single mums and single dads.
"If you have a student in a support unit and have another child who can't go to the same school, you then have to rely on other people, buses, taxis or even Ubers to get children where they need to be."
Ms Car said the policy was a "bad decision" from the government.
"The Liberal Government began this enrolment crackdown without consulting with parents and school communities and without assessing the impact on busy working families and families with children with learning support needs," she said.
"The Liberal Government is causing families in Campbelltown and across Sydney undue stress with this unfair enrolment crackdown."