In a new report, the Claystone think tank says it has evidence that they're being disproportionately singled out.
In recent years Oftsed has looked to ensure schools are promoting 'British Values' - a set of ideals which have been set up to bring about better social cohesion.
Claystone says these are very narrow set of poorly understood values and those deemed to not be implementing these values can be closed down.
Speaking to Premier, report author Dr Umer Siddique suggested there's no valid reason for targeting people of faith.
"There isn't any correlation between holding socially conservative values and violent extremism," he said. "Some studies actually suggest being more devout is actually a protective factor."
Dr Siddique says that while Muslim schools are faring the worst when it comes to no-notice inspections, Christian and Jewish schools are also being targeted.
Ofsted told Premier in a statement: "Ofsted holds all schools to the same standards, regardless of their ethos.
"Ofsted inspects independent schools at the request of the Department for Education (DfE). All independent schools have to meet the Independent School Standards. These are regulations set by the DfE. The independent school standards set out basic expectations about what schools should do to ensure that pupils receive a broad education and are well prepared for life in Britain society."
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