The board of

Affiliated Computer Services

(ACS)

authorized up to $1 billion for a share repurchase program on Monday.

The open-ended program to repurchase Class A common stock is effective immediately. The plan represents about 18% of ACS total outstanding shares.

ACS said it will buy its shares on the open market from time to time, based on its level of cash and debt balances, the general business environment, and alternative investment opportunities, among other factors.

In the after-hours trading session, shares of the IT services firm lifted 0.6%, or 26 cents, to $47. During market hours, the stock sunk 3.3%, or $1.57, to close at $46.74.