"All bus traffic is suspended until further notice in order to prevent infection," the city's KMG public transport operator announced.
The company runs all public transport in the southern city of 100,000 inhabitants, which is also the state capital of Carinthia.
It took the unusual measure after it was revealed that one driver had been diagnosed with measles on 3 April.
Since then two further suspected cases have been reported.
KMG said it was working to establish "the vaccination status of all drivers" before authorising bus services to restart and was embarking on a deep clean of its vehicles.
The resurgence of measles, a once-eradicated and highly-contagious disease, is linked to a growing anti-vaccine movement in richer nations -- which the World Health Organization has identified as a major global health threat.
On Tuesday, New York mayor Bill de Blasio declared a public health emergency in parts of the city, ordering all residents of certain districts in Brooklyn to be vaccinated to fight a measles outbreak concentrated in the
ultra-Orthodox Jewish community.