Hertz Global Holdings (HTZ) adopted a one-year shareholder rights plan to ward off investors looking to amass a large stake in the car-rental giant.

The company said the move stems from “unusual and substantial” trading activity. The so-called poison pill has a 10% trigger, reducing the chances that any individual shareholder or group can gain control of Hertz by buying up shares.

Hertz added that although it doesn’t comment on specific discussions with shareholders, the company “has had dialogue with a number of shareholders and welcomes their input towards the goal of enhancing shareholder value.”

The largest Hertz shareholder is Wellington Management Co., which has a stake of nearly 9.2%. Vanguard Group, Fidelity Management & Research Co. and T. Rowe Price Associates round out the top four holders.

Shares of Park Ridge, N.J.-based Hertz jumped 8.9% to $28.22 late Tuesday morning.

The stock added to earlier gains after a news report that Daniel Loeb’s hedge fund, Third Point, took a new stake of less than 5% in Hertz.

A spokeswoman for Third Point declined to comment. Hertz didn’t immediately respond to an inquiry from FOX Business.

Hertz was already up 59% on the year through Monday’s close, easily outpacing the broader market as 2013 comes to a close.

Rival Avis Budget Group (CAR), which has soared 99% year-to-date, rose 2.1% to $40.34 on Tuesday.

Both car renters have benefited from a rebound in leisure and business travel over the past few years. Hertz, the No. 2 U.S. car rental company behind privately held Enterprise Holdings, completed its acquisition of Dollar Thrifty about a year ago. Avis completed a buyout of Zipcar in March.

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