The nation's investors slammed American International Group ( AIG) after a stock split the company's investors overwhelmingly approved.

Shares of the insurer tanked 21% to $18.22 in afternoon trading, a day after shareholders approved a 1-for-20 reverse stock split to boost share price.

Before the split, AIG's shares closed Tuesday at $1.16 a share.

At AIG's annual meeting on Tuesday, shareholders approved the company's proposal to lift the share price by shrinking the number of outstanding shares at a ratio of 1 for 20. Thus, investors who held 1,000 shares of AIG will now own 50.

When the proxy proposal was disclosed in May, CEO Edward Liddy said a split would protect the company's listing on the New York Stock Exchange.
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