Bulgaria's Parliament has adopted changes to automobile transportation law which obligate taxi drivers to have certificates showing they work under contracts of employment, and not on their own account.

The amendments have been passed at both first and second readings.

Until now, taxi driver were able to offer transport services on behalf of a certain company without being employed by it.

Critics of the new wordings have called them "anti-Uber" changes and have pointed that they coincide with a ban on carhire service Uber's operations in Sofia upheld by the Sofia Administrative Court last week. The company's rapid expansion in the Bulgarian market has been met with resistance from taxi drivers who complain about losing customers.

MPs from the main ruling GERB party have argued the new version of the bill will allow for stricter control on taxi drivers and companies, with the latter being increasingly forced into offering employment contracts to drivers.

Bulgarian officials have repeatedly pointed out that Uber's mode of not employing its drivers and offering paid transportation services done using unregistered vehicles are not allowed under Bulgarian law.

The fine imposed on Uber so far, however, has only been with regard to a breach of competition rules.

Uber maitains it is halting activities in Bulgaria only on a temporary basis, short of withdrawing from the market. On Tuesday it launched a petition calling on citizens to stand up for "their right to choice" and to demand that authorities revoke the ban on its operations.

Defenders of the changes, on the other hand, say they will also address illicit practices among taxi drivers, making them illegal. A highly cited example is the malpractice of drivers using the cab of a certain taxi company on their own behalf, after having been granted the right to do so, and setting prices much higher than the average ones or manipulating taxi counters.