Sky shareholders are demanding guarantees from Sky that its proposed buyback of 5% of its shares will not result in News Corp reneging on its promise to cap its voting stake in BSkyB at 37.14%.
News Corp's share would rise to more than 39% following the buyback.
The buyback will be among the resolutions put to shareholders at BSkyB's November 4 annual meeting.
News Corp said in August that it was extending its "poison pill" provision for a further two years to prevent John Malone's Liberty Media from increasing its voting stake in the company beyond 18%.
The "poison pill" was due to expire in November, but when News Corp reported better-than-expected annual results, the board said it would be extended for another two years.
The strategy blocks investors from taking their voting shareholding beyond 15% and existing shareholders with stakes above 15% are prevented from adding to their holdings.
Eleven pension funds have issued a suit to News Corp chairman Rupert Murdoch about the poison pill plans, saying the move jeopardises the financial security of all shareholders in News Corp.
BSkyB UK shareholders are concerned News Corp will do the same here and have demanded a statement from BSkyB or News Corp that the voting stake will not be increased beyond the cap.
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