The board of Unum Group Corp. (NYSE:UNM) has agreed to spend up to $500 million more on buying back the company’s common stock over the next 12 months.

Unum ended the first quarter with about 332 million shares of common stock outstanding, and shares have been selling for about $20 to $25 per share.

Unum may make repurchases either in the open market or through privately negotiated transactions, the company says.

The Unum board has reserved the right to modify, extend or cancel the stock buyback program.