For the past six years, energy companies and Maine residents have been in a fierce stand-off over the construction of a 53-mile power line extension that would deliver 1,200 megawatts of renewable hydroelectric power from Canada to Massachusetts, which is enough to power approximately 1.2 million homes. For two-thirds of the distance, the electricity would follow a transmission line corridor which already exists. But without the 53-mile, 54-foot-wide extension, the $1 billion construction project is a at an impasse. The power line has already received all of its state and federal permits. But in a state-wide vote in November, Maine voters rejected the project. Now, the constitutionality of that referendum vote is being battled out in court and will be decided this summer, according to Anthony W. Buxton, the lawyer representing the power companies that want to complete the transmission line. If the Maine court system rules that the referendum vote was unconstitutional, then the energy companies involved can continue construction.