Hedge fund Toms Capital Investment Management is escalating its campaign for asset manager Voya Financial to evaluate strategic alternatives, including a potential sale, by taking its case directly to shareholders. In an open letter to be sent Thursday, TCIM reveals it holds a roughly 4.5% stake in Voya, making it one of the company's largest shareholders. Voya has a market value of around $9 billion, and its shares have climbed more than 30% over the past 12 months, driven partly by takeover speculation.

TCIM has been privately urging Voya for months to explore a sale or other strategic options, but those efforts have been unsuccessful, according to the letter. The firm now plans to rally fellow shareholders to pressure the board into action. Voya has not publicly responded to the latest push.

The activist campaign highlights growing investor impatience with Voya's standalone strategy despite the stock's recent rally. TCIM argues that a sale would unlock greater value for shareholders than the current trajectory.