Dec 2 (Reuters) - ACI Worldwide Inc should consider selling itself to maximize value as the payments industry faces consolidation, activist investor Starboard Value said on Wednesday.

Starboard, one of ACI's largest shareholder with a roughly 9% stake, asked the company to hire advisers and conduct a sale process one month after management presented conservative revenue growth and margin targets at its investor day.

Starboard said management's long-term plan may create value, but that it would take too long and could be too risky to justify plans for ACI to remain a standalone company.

"If this new guidance is really the best that you can do over the next three years, then we believe that a sale of the Company is clearly a more attractive option for shareholders," Starboard wrote to ACI, in a publicly released letter.

Shareholders reacted to Starboard's increased pressure by pushing ACI's shares up roughly 11% to $36.91.

The company said it is "operating with a sense of urgency to maximize profitability, approach operations with renewed cost discipline, and identify all opportunities for compelling growth and value creation." A spokesman also said ACI has active communications with shareholders and that it is making "substantive progress in executing (its) three-pillar strategic plan."

Two months ago Starboard called ACI an "attractive" takeover candidate, adding that it has underperformed peers including Blackbaud Inc, Commvault Systems and FireEye Inc.

M&A activity in the payments sector has accelerated over the last years as companies need scale amid the increasing complexity and technology requirements of ecommerce. Last month European payments processor Nexi SpA said it would buy Net A/S from a group of private equity investors.

ACI itself may have been approached by potential buyers in the past, Starboard said.

Starboard, which won 17 board seats at four companies in the first half of 2020, has until early March 2021 to decide whether it wants to nominate directors. (Reporting by Noor Zainab Hussain in Bengaluru and Svea Herbst in Boston; Editing by Kirsten Donovan and Leslie Adler)