Hungary on Thursday became the latest European Union country to launch a probe into Uber, the popular but controversial taxi app for mobile phones.
"A tax audit of the local unit of ridesharing company Uber has been ordered," the economy ministry said in a statement.
"Uber is operating in Hungary without paying any substantive taxes and often failing to comply with rules governing the taxi profession," it said.
Uber puts customers in touch with private drivers at prices lower than those of traditional taxis but is facing legal challenges and limits on its activities.
Taxi firms are furious because they say Uber drivers should be regulated the same way as normal cabs.
Uber earlier this month filed complaints with the EU against France, Germany and Spain, hitting back at efforts to ban it from the continent's streets.
Uber said efforts by national governments to shut it down breached EU laws on competition and the single market.
In Budapest, Uber advertises a base fare of 300 forints (0.98 euros, $1.11) and 130 forints per kilometre.
Under a decree in force from last September, the base fare for taxis operating in Budapest was set at 450 forints and the per kilometre fee at 280 forints.