Halts and Resumptions:

A trading halt is the temporary suspension of trading in a security of a publicly listed company, usually in anticipation of a material news announcement by the company. The halt in trading allows the company time to release its announcement and for the market to absorb the information. The stock typically doesn't resume trading again until the company releases information on their stock.

The decision to halt trading for dissemination of material news in a particular company is made by IIROC. Longer trading halts for business reasons such as non-filing of fees or for detailed review of filings is made by the Exchanges.

Why trading halts are necessary
Trading halts are based on the principle that all investors should have the same timely access to important company information. A trading halt gives all investors equal opportunity to hear the news and make any appropriate trade decisions (buy, sell or hold) based on that information. During a halt, brokerage firms cannot buy or sell the halted company's securities.

A trading halt can be initiated by a listed company, the marketplace or IIROC. When the company involved makes the request, which is often the case, the company has information to disclose about its business or financial affairs that it expects could lead to a significant change in the market price of its listed securities. The company must provide assurance to IIROC that a material announcement will be made imminently after a trading halt is imposed.

Length of a trading halt
A trading halt is normally very temporary - typically lasting less than two hours. The actual length of a trading halt is determined by IIROC, taking into account the significance of the company's announcement and the amount of time required to disseminate the announcement. Under normal circumstances, trading resumes within approximately one hour following the company's announcement through the major news services. IIROC will issue a trade resumption notice when a halt is lifted. In some cases halts are extended by IIROC to companies to release more complete information.

Exchange (Business) Halts
Halts longer then a few hours are usually business halts put in place by the Exchanges due to an ongoing review or for a business reason such as non-payment of fees.