Trai sent out fresh set of questions to both Bharti Airtel and Vodafone Idea on July 31, and the operators have been asked to respond to the questions on August 4.
Emails sent to Bharti Airtel and Vodafone Idea did not elicit a response.
Trai has said it is desirable that points raised in the questionnaire be covered in a presentation scheduled on the issue on the same day. The regulator has asked the companies to back their claims via data, the source said.
A Trai official said that the previous responses received from companies were "vague" and gave no real assurance to address regulator's concerns over whether network preference to specific customers resulted in deterioration of services for other non-premium subscribers.
The regulator wants the companies to demonstrate certain claims made by them that there is no adverse impact of the said premium/platinum plans on network experiences of general customers.
If operators can prove that they can indeed guarantee some speed to certain types of subscribers, then the regulator could mull getting into setting quality standards for non-premium subscribers as well, the official said.
Earlier this month, the two telcos responded to Trai's previous round of questioning where they vehemently defended their priority plans, and argued that the offers have nor degraded network experience of non-premium users nor flouted any regulations. They said the subscribers of the plans constitute only a small portion of overall customer base.
In a letter to Trai, Vodafone Idea had said the benefit featuring network priority "is fully compliant to all applicable tariff orders and regulations" and that "Trai has prejudged and prematurely concluded poor network service".
On July 17, the telecom tribunal had stayed Trai's order on Vodafone Idea, which had asked the company to withhold its offering promising priority 4G network on RedX plan.
At the same time, the Telecom Disputes Settlement and Appellate Tribunal had said it would be open for Trai to proceed with the inquiry and pass final orders in accordance with law at the earliest after ensuring that requirements of natural justice are satisfied.