TOMEI International's bid to take control of Yanion International Holdings is facing a challenge from anonymous minority shareholders of Yanion, who have called for a vote against the takeover. In an open letter to Yanion shareholders, it was alleged that Tomei, under the takeover proposal, would acquire Yanion without paying a substantial premium to the company's net asset value. The minority shareholders urged other shareholders to vote at a special general meeting on Monday against the proposed issue of 382 million new shares at 41 cents each to Tomei. If the issue was approved, Tomei would hold a 51 per cent stake of the enlarged share capital of Yanion, and a general offer would be made by Tomei at the same price. The open letter claimed that the offer price of 41 cents represented a substantial discount of 21.2 per cent to the market price of 52 cents, and a 32.8 per cent discount to the average traded price so far this year of 61 cents. The offer price was also at an 8.9 per cent discount to the net asset value of 45 cents a share, as at December 31 last year, the opposing shareholders said. They questioned whether the deal was on normal commercial terms. They expressed concern that the controlling shareholders were in favour of ''an apparently un-commercial transaction'' and were acting in concert with Tomei to deliver control. ''Allowing the controlling shareholders to vote would be contrary to the spirit of the takeover code and the listing rules,'' said the shareholders. They requested that an independent financial adviser examine at the deal. ''Before receiving such independent advice, shareholders can not be fully informed, and without it, they can not be sure they are not being abused,'' they said.