IIROC can make a decision to impose a temporary suspension (halt) of trading in a security of a publicly-listed company. Trading halts are implemented to ensure a fair and orderly market. IIROC is the national self-regulatory organization which oversees all investment dealers and trading activity on debt and equity marketplaces in Canada.
SOURCE Investment Industry Regulatory Organization of Canada (IIROC) - Halts/Resumptions
Read more at http://www.stockhouse.com/news/press-releases/2015/04/28/iiroc-trading-halt-pnp-db#dBfBCB2HkobLgzCG.99