NEW YORK, June 29 (Reuters) - U.S. Senator Angus King is urging the country's top energy regulator to reject NextEra Energy's ( NEE ) proposed $66.8 billion acquisition of Dominion Energy ( D ), saying the deal would consolidate too much power in the hands of one company, a filing on Monday showed.

The country has seen a spate of giant power mergers in recent years with the rise of electricity demand after a roughly two-decade-long lull, driven by the expansion of energy-intensive data centers and the electrification of industries like transportation.

Last month, NextEra announced its plan to buy Dominion to create the world's largest regulated electric utility, in what would be one of the all-time biggest mergers of its kind. Virginia-based Dominion serves the largest concentration of data centers globally.

In a letter to the Federal Energy Regulatory Commission, King, from Maine, said the massive utility formed by the consolidation would deter competition in a territory that would affect more than 10 million people.

"A single firm with that mix of merchant generation, regulated generation, transmission, and load-pocket exposure has powerful incentives and tools to shape regional markets in its favor," King said, citing the 110 gigawatts of electric-generating capacity between the two companies, the most natural gas-fired power and second-largest nuclear operations in the country.

King said NextEra has already stymied clean energy power competition through lobbying efforts in New England. He cited other business conduct concerns by the company that he said could ultimately raise prices for consumers.

NextEra was not immediately available for comment.