T-Mobile on Monday announced its second wind power contract and vowed to use renewable power to account for 100 percent of its energy use by 2021.

The company also became the first U.S. carrier to join the RE100 initiative, whose members vow to meet those renewable energy thresholds. As of Tuesday, 123 companies had joined RE100, including tech giants Apple, Google and Microsoft and overseas telecom companies BT, KPN, Proximus and Telefonica.

"As a large electricity consumer in the U.S., they can truly transform energy systems by bringing significant renewable capacity online — all of that while delivering real value to their customers," Sam Kimmins, who heads RE100 at The Climate Group, said of T-Mobile.

The carrier's first wind power project began operating in Oklahoma last month, and the company detailed an agreement with Infinity Renewables to support a second wind project in Kansas.

Once the second project begins operating in 2019, the combined 320 MWs of electricity would meet about 60 percent of the company's domestic energy needs. T-Mobile plans to purchase wind power to account for the remaining share.

CEO John Legere called the commitment "the right thing to do" and added that it is expected to trim the company's energy costs by "around $100 million in the next 15 years."

The company also pledged to donate $500,000 to a clean energy nonprofit and vowed to add another $500,000 each if larger U.S. rivals Verizon and AT&T match its renewable energy commitment.

“We’re going to drag the other guys kicking and screaming into the clean power future," Legere said in a statement.