Shin dropped 0.85 per cent to Bt29, AIS 2.29 per cent to Bt85.50, ShinSat 2.08 per cent to Bt7.05 and iTV 2.82 per cent to Bt2.76.

The prices dropped even though Shin and the three subsidiaries yesterday sought to clarify that a lawsuit seeking revocation of their concessions was filed by an individual citizen against government authorities for not fulfilling their duties and did not involve them.

In separate filings to the Stock Exchange of Thailand, Shin, AIS, ShinSat and iTV said the case was not a concession dispute between the subsidiaries and the granters of their concessions and that they would continue to operate as usual.

On Thursday, the Supreme Administrative Court ordered its lower court to consider a case filed by Rangsit University law lecturer Sastra To-on. Sastra alleged that the Information and Communications Technology Ministry, TOT Plc, the Prime Minister's Office and the Transport Ministry had been neglectful in not revoking Shin concessions after the company was sold to Singapore's Temasek Holdings in January.

He originally filed the lawsuit with the Central Administrative Court in March, but the lower court refused to accept the case on the grounds that Sastra was not personally affected by the Shin sale.

The Supreme Administrative Court reopened the case after deciding that as a customer of the companies involved, Sastra was affected by the sale, because the transfer of the existing concessions to an "alien" firm could downgrade the services provided by the companies.

Following the court's agreement to prosecute the case, some securities houses advised clients to refrain from buying the four stocks, due to the uncertainties involved. But others were still advising investors to purchase the shares - except for iTV stock - in the belief that the ruling would not eventually lead to licence revocation.

Ayudhya Securities is in the second camp. It believes the Central Administrative Court's ruling will indirectly define whether Kularb Kaew Co Ltd is a nominee. If Kularb Kaew were found to be a nominee, that would subsequently 'raise the foreign shareholding in Shin and its subsidiaries'.

On this assumption, iTV could lose its concession, because the foreign shareholding would exceed the statutory limit of 25 per cent, while AIS could be ordered to bring down the foreign shareholding to 49 per cent. Meanwhile, ShinSat would be off the hook.

Even in the worst-case scenario, the ruling should not result in the cancellation of the current concession given to ShinSat, because the satellite concession did not set a limit on foreign shareholders. Its foreign shareholding would not rise above 49 per cent even if Kularb Kaew were defined as a nominee, because the current level is only 3 per cent.

But even if AIS's foreign shareholding could rise above the 49-per-cent limit set by law, from 48 per cent at present, it should be eligible to keep its concession, because TOT itself did not set a foreign-shareholder limit.

However, it may need to lower the foreign shareholding if it wants to win new business licences, particularly for third-generation services, from the National Telecommunications Commission.

iTV is likely to be the most vulnerable from the ruling, because the iTV concession stipulated clearly that foreign juristic persons were not allowed to hold more than 25 per cent. Therefore, this past Thursday's hearing may eventually lead to the revocation of its license, says Ayudhya Securities.