Fares for electric train lines could rise under the new common ticketing system if the government does not provide more subsidies for private companies which operate the lines in Bangkok, BTS Group Holdings Plc chairman Keeree Kanjanapas says.

He said several companies are set for higher operating and maintenance costs due to higher passenger numbers and route expansions.

"Every private operator would naturally want to use their own starting prices," Mr Keeree said.

"If the MRT and BTS each observes separate, one-baht starting fares, for example, how will the common ticketing system implement a collective starting price for less than that amount, without further concessions first being given to the operators by the government?"

Upon its completion, the common ticketing system aims to allow passengers to use a single card -- called the "Mangmoom," or Spider card -- to access all modes of transport.

However, the system's integration has been postponed several times, with the latest statement by the Transport Minister pushing the cards' official rollout to June 2018.

The June deadline will see the public initially use the Mangmoom cards to transit between the Airport Rail Link and public buses, while the BTS skytrain and MRT Purple and Blue Lines are expected to follow through in October, he said.

Authority for the common ticketing system was transferred from the Office of Transport and Traffic Policy and Planning (OTP) to the Mass Rapid Transit Authority of Thailand (MRTA) earlier this year, as a result of a cabinet decision.