Leading operators Reliance Communications, Vodafone India and Idea Cellular could lose sizeable chunks of their revenue if they don’t win back their existing spectrum in certain regions during next year’s spectrum auction, according to Economic Times.

Separately, the same three operators are among those Indian companies to have been issued with so-called “show-cause” notices for under-reporting their sales, the country’s Telecom Minister, Ravi Shankar Prasad, told the country’s parliament.

Reliance Communications, Vodafone and Idea could lose as much as 27 per cent, 18 per cent and 15 per cent of their revenue respectively if they are unsuccessful in the 2015 auction, based on data from regulator Telecom Regulatory Authority of India (TRAI).

They are likely to face competition in the auction from rivals including market leader Bharti Airtel and aggressive newcomer Reliance Jio Infocomm.

The government is set to auction airwaves in the 900 MHz and 1.8 GHz bands across 18 of India’s 22 telecom services areas early in 2015.

The sale is happening with the 900 MHz frequencies because of the expiry of operators’ 20-year licences. Those in the 1.8 Ghz band are frequencies left unsold from February’s auction.

With regard to the show-cause notices for misreporting revenue, Dishnet Wireless, Aircel, Tata Teleservices and Bharti Airtel also stand accused of the same offence, according to the Department of Telecommunications.

All the companies deny the charge and have made representations to the ministry, which has yet to make a final decision.