For their part, the listing U.S. stock exchanges have the authority to halt trading based on their evaluation of a given announcement. Generally, the more likely the announcement is to affect the stock price, whether positively or negatively, the more likely the exchange is to call for a trading halt pending dissemination of news by the issuer. An exchange can also halt trading after news affecting the company has been released. This could happen when the company releases information without notifying the exchange in advance—or when another company announces an unsolicited tender offer for the company whose stock is now subject to the trading halt. In very rare instances, an exchange may choose to halt trading when, regardless of the timing of any announcement, a high-impact event outside the company’s control occurs—such as an unforeseen natural disaster or a significant market disruption—that can affect trading in a stock.