By owning a share, the shareholder owns a percentage of the company whose share s/he owns. A share, however, does entitle the shareholder to a specific percentage ownership; the amount of the company that the shareholder owns is dependent of the number of shares owned and the number of shares outstanding. If Jim owns 10 shares of Oracle, and there are 1,000 shares outstanding, Jim effectively owns 1% of Oracle. If the number of shares outstanding were to double to 2,000, Jim's 10 shares would now correspond to a 0.5% ownership stake. In order for Jim's ownership stake to remain constant, the number of shares he holds must change in proportion to change in outstanding shares: he must own 20 shares if there are 2,000 shares outstanding.
That is the premise behind a reverse stock split. In a reverse stock split (also called a stock merge), the company issues a smaller number of new shares. New shares are typically issued in a simple ratio, e.g. 1 new share for 2 old shares, 3 for 4, etc.
The reduction in the number of issued shares is accompanied by a proportional increase in the share price. A company with a market capitalization of $1,000,000 from 1,000,000 shares trading at $1 chooses to reduce the number of outstanding shares to 500,000 through a reverse split. This leads to a corresponding rise in the stock price to $2.
There is a stigma attached to doing a reverse stock split, so it is not initiated without very good reason and may take a shareholder or board meeting for consent. Many institutional investors and mutual funds, for example, have rules against purchasing a stock whose price is below some minimum. In an extreme case, a company whose share price has dropped so low that it is in danger of being delisted from its stock exchange, might use a reverse stock split to increase its share price. For these reasons, a reverse stock split is often an indication that a company is in financial trouble.
A reverse stock split may be used to reduce the number of shareholders. If a company completes reverse split in which 1 new share is issued for every 100 old shares, any investor holding less than 100 shares would simply receive a cash payment. If the number of shareholders drops, the company may be placed into a different regulatory categories and may be governed by different laws .
SEC
The Securities and Exchange Commission is the department that sets the different regulations regarding stock trading and splitting.