Parkinson brokered a deal with Sunflower in May, allowing one new coal-fired plant and passage of legislation aimed at promoting renewable energy and conservation, something that had been blocked by lawmakers who supported the utility's effort.
Sunflower then reapplied for an air-quality permit last month.
In a letter to Bremby, William Rice, the Environmental Protection Agency's acting regional administrator in Kansas City, said the state must treat the proposal as a "new project."
Earthjustice, a national group that still hopes to block the new coal plant, saw Rice's letter as a victory and believes it could delay construction 18 months.
But Sunflower spokeswoman Cindy Hertel said the utility already anticipated some delay and that Rice's letter contained nothing surprising. She noted that Sunflower's CEO already had predicted construction might not start for up to 18 months.
Sunflower promised to work with both state and federal officials, and Hertel said it would submit additional material to the state this fall.
EPA spokesman David Bryan said the agency wants to make sure the public has an opportunity to comment before the Kansas Department of Health and Environment decides whether to issue an air-quality permit.
"The fact that we believe it's a new project triggered what we did," Bryan said. "Our biggest concern is that it hasn't had a public airing yet."
Bryan noted that the EPA has oversight of Kansas' permitting program - and the power to issue an order to stop construction of a coal plant.
Kansas Department of Health and Environment spokesman Mike Heideman said the state agency hadn't seen Rice's letter, and he would not speculate about how the department might respond.
As for Parkinson, spokeswoman Beth Martino said: "The governor supports the regulatory process and trusts the agencies responsible for that process to administer it."
Amanda Goodin, an Earthjustice attorney in Seattle, saw Rice's letter as a sign of "a new day at EPA," following last year's election of President Barack Obama. He's pursuing legislation to cut greenhouse gases linked by many scientists to global warming.
Earthjustice and the Sierra Club sent their own letter to Bremby, demanding public hearings on Sunflower's plan.
"It's really the EPA telling Kansas to step in line," she said. "We don't think the outcome is predetermined."
Sunflower had previously sought to build two, 700-megawatt coal-fired electric plants next to an existing one outside Holcomb. The new plan calls for an 895-megawatt plant, with enough capacity to meet the peak electricity needs of 448,000 households, according to one state estimate.
As part of its deal with Parkinson, Sunflower agreed to pursue measures to offset potential CO2 emissions and to develop wind energy.