A rally in Sydney on Saturday protesting cuts to healthcare got heated when members of the crowd chanted 'let them stay' during a speech at Town Hall by Labor leader Bill Shorten.

Protesters chanted the catchphrase as Mr Shorten criticised the federal government's proposed plan to cut funding from pathology and imaging services, including pap smears.

The Opposition Leader spoke of Medicare as a "fundamental Australian value", warning the crowd of a Liberal government's plan to "Americanise" the healthcare system.