Express Scripts (ESRX) is attempting to resist the entry of a potential buyer. The company has received an unsolicited "mini-tender" offer for a block of its shares from TRC Capital, which has offered to buy up to 2 million shares of the company, roughly 0.24% of the outstanding amount, at $55.75 apiece.

Express Scripts is recommending that its shareholders reject the bid. It pointed out that TRC Capital's offer was nearly 3% below the stock's closing price of $57.27 on April 8.

TRC Capital is known for its use of "mini-tender" offers, a practice that has aroused some controversy. Since such bids are for less than 5% of a company's stock, they avoid numerous SEC procedural and disclosure requirements.