BEIJING, Jan. 7 (Xinhua) -- The outcome of a vote to approve China Eastern Airlines' (CEA) sale of a stake to Singapore Airlines (SIA), scheduled on Tuesday, is up in the air after a major shareholder made a counter-bid, effectively voting against the deal.   China National Aviation Corporation (Group), or CNAC, said in a statement late Sunday that it would offer at least 5 Hong Kong dollars (0.64 U.S. dollars) a share for the stake in CEA if shareholders rejected SIA's bid of 3.8 Hong Kong dollars apiece. Hong Kong-based CNAC, which holds 12.07 percent of China Eastern's H shares, is a wholly-owned subsidiary of China National Aviation Holding Company (CNAHC), the Beijing-based parent of Air China. CEA had agreed to sell 1.88 billion H shares, or 24 percent of the expanded capital, to SIA and Lentor Investments, a unit of Temasek Holdings. Temasek is an investment company owned by the Singapore government. CNAC objected to the deal last week by raising the possibility of a counter-bid at an unspecified price and said the SIA offer did not reflect the fair value of CEA. According to estimates published in the Shanghai Securities News, CNAC would have to pay 14.9 billion Hong Kong dollars for the stake in the Shanghai-based airline, calculated at 5 Hong Kong dollars a share. The offer was 3.58 billion Hong Kong dollars more than the Singaporean bid. CNAC also proposed in the Sunday statement to buy shares originally offered to CEA's parent company, CEA Holding, which had promised to have no more than 30 percent of CEA's shares. Under Hong Kong securities rules, a 30-percent stake in CEA would lead to the purchase of CEA by CNAC. The statement had ruled out that possibility. Analysts said this declaration indicated CNAC's resolution to buy shares from CEA. CEA, however, responded by expressing doubt over several issues, such as whether CNAC actually had the funds for the deal. Observers quoted by the newspaper said that CNAC's Sunday statement was apparently timed to influence smaller investors to vote against the SIA deal on Tuesday. Saturday's China Securities Journal reported CEA's negative attitude towards CNAC's possible counter-bid had drawn complaints from many small and medium-sized shareholders, who said that the airline had failed to take into consideration their interests by blocking potential higher bids. CNAC argued in its statement that its higher-price offer would be more helpful in light of CEA's tight financial situation and would be in the interests of all of its shareholders. CNAC said it would submit the bidding plan to China Eastern in two weeks, but it agreed the plan was still subject to approval by regulators and CEA shareholders. Amid escalating competition among dome