The company called the offer "inadequate" and said it "fails to take into account PeopleSupport's strategic value and success in implementing its growth strategy."

PeopleSupport said the best way to enhance shareholder value is to implement strategic plans already in place, which include investing in its sales organization, expanding its service offerings and increasing prices.

IPVG and AO Capital Partners offered last month to buy the company for $15 per share, which represented a premium of about 18 percent to the stock's closing price the day before the offer was announced.

IPVG, based in the Philippines, operates information technology and BPO businesses, while AO (American Orient) Capital Partners offers investment banking services.

PeopleSupport shares rose $1.33, or 9.7 percent, to $15.10 in electronic after-hours trading. During regular trading, shares rose 20 cents to close at $13.77. The stock has traded in a 52-week range of $8.19 to $24.41.