A publicly traded corporation follows a different procedure.  The percent needed for an acquisition, buy-out, merger, divestiture, etc. is outlined in the company's by-laws or other formation documents.  However, since it is a publicly traded company, and there may be thousands or even millions of shareholders, it usually must hold a shareholder meeting to vote on the proposed transaction.

Furthermore, not only will a state's laws dictate some of the rules and procedures necessary for a merger or acquisition, but federal law also plays a significant role.  The government is involved in these transactions to ensure that there are no anti-trust violations, or other situations that could pose a threat that weakens competition, creates a monopoly, etc.

Much legislation has been enacted over the last century or so that has shaped the landscape of the U.S. corporate world, the markets, and the economy as a whole.  The most well-known antitrust acts include the Sherman Act and the Clayton Act.  Furthermore, the federal agencies regularly involved in mergers and acquisitions include the Federal Trade Commission and the U.S. Department of Justice.  

The complexities involved for any business transaction require the expertise of a highly skilled attorney.  If you are thinking of approaching another entity for a merger or acquisition, or if you have been approached, you are likely to need a mergers and acquisitions attorney.  He or she can help evaluate your business, the effects of the transaction, and generally whether or not the deal would benefit your organization.