UK bookmaker William Hill is throwing a wrench into Scientific Games Corporation’s proposed acquisition of online gambling technology provider NYX Gaming Group.

On Wednesday, the Toronto-listed NYX informed the markets that a division of William Hill – a major NYX shareholder – had asked to convert its NYX convertible preference shares into ordinary shares by December 4 in order that Hills could vote against Sci-Games’ proposed purchase of NYX. The vote on the C$775m (US $631m) deal is scheduled for December 7.

Hills contributed roughly £90m to the £270m price that NYX paid to acquire sports betting technology firm OpenBet in April 2016. OpenBet powers Hills’ sports betting platform, and the investment was seen as a way for Hills to ensure it remained a priority customer for OpenBet.

NYX’s statement claimed that Hills would only vote in favor of the Sci-Games takeover if Sci-Games first signed a commercial arrangement that ensured continuity of Hills’ sports betting operations. Failure to reach such an arrangement would mean that Hills “will vote against and therefore effectively block” the acquisition.