Not satisfied with their replies, telecom regulator TRAI has sought additional information from leading service providers, including Bharti airtel and Vodafone, on their recent decision to hike mobile tariffs by up to 20 percent.

"TRAI has received replies from various operators and we have asked for some more inputs from some of the service providers for their reasons to hike tariffs," a TRAI source said.

Earlier, the Telecom Regulatory Authority of India (TRAI) had sent letters to all the companies that recently hiked tariffs, seeking their justification for the tariff hike.

Companies like Bharti airtel, Idea Cellular, Vodafone and Reliance Communications recently raised tariffs for their services by about 20 percent in most operating circles. Most of the companies cited inflationary pressure in the country as being responsible for the tariff hike.

Industry experts are of the view that the hike in mobile tariffs is anti-consumer and it will only result in an abnormal increase in companies'' profits. Most of the operators have been given spectrum free of cost so that they can provide affordable services.

TRAI, a source said, would also look into this aspect before taking any decision.

Airtel had raised the tariffs for its 'Advantage' and 'Freedom' pre-paid tariff packages, which are based on per minute billing, to 60 paise per minute for local and STD mobile-to-mobile calls. Earlier, it was 50 paise per minute in this category.

"Telecom is probably the only industry where, despite increasing inflation, tariffs have been falling unabated. Continuously declining margins, high 3G and BWA auction prices, constrained spectrum and rural roll-out aspirations leave us with little choice but to make some price corrections," Bharti airtel had said in a statement.