S-13.1, r. 3 - By-law respecting casino games

Full text
23. A player may double down if his first 2 cards total 9, 10 or 11. In such a case, he receives only one additional card. Moreover, he cannot double down his bet if his 2 first cards are an ace and a face card or a ten.
O.C. 1253-93, s. 23.