CHARLOTTE, N.C. (AP) â¿¿ Environmental activists on Thursday blocked a train shipment of coal to a Duke Energy Corp.'s plant outside of Charlotte. The action took place the same day the utility company is holding its annual shareholders meeting in North Carolina's largest city. Greenpeace spokeswoman Molly Dorozensk said four activists handcuffed themselves to tracks, while others draped banners with Apple's logo on freight cars. Apple is building a data center in the state. Environmentalists say Duke Energy is using that site and other massive data centers in the state to justify investment in coal-fired plants. It took authorities about three hours to remove the demonstrators from the tracks. The train was taking coal to the company's Marshall steam plant, which is the company's second-largest coal-powered plant in the Carolinas. Six people â¿¿ including the four who had chained themselves to the tracks â¿¿ were arrested by Catawba County sheriff's deputies. Dorozensk said she didn't know what charges they faced. Telephone calls to the Catawba County sheriff's office were not immediately returned. Duke Energy spokeswoman Paige Sheehan said the protesters' claim that the company was using data centers to build new coal plants was wrong. She said the company was building coal plants to retire old ones. She noted that Cliffside, where the company is building a $2.4 billion coal-fired generator, is a top-of-the-line plant. "We built Cliffside so it could retire old coal plants and comply with new, strict environmental rules," she said. Greenpeace contends the use of coal is creating an environmental hazard, and that coal mining is damaging the ecology of the Appalachia region. Meanwhile, about 50 people demonstrated outside Duke Energy's headquarters before the shareholders meeting. They said they showed up despite new city restrictions to control demonstrations. The city in January adopted an ordinance allowing it to declare public gatherings as extraordinary events. That allows the city to create extraordinary event zones â¿¿ designated areas where people won't be allowed to carry backpacks and other items.