The Environmental Protection Agency sent an anticipated greenhouse gas emission rule for existing power plants to the White House for federal review Tuesday, a move that would round out a cornerstone of the president's climate agenda.

The EPA sent the rule to the Office of Management and Budget for review. The agency plans to finish the rule by June 2015.

Public health and environmental groups say the measure would save billions of dollars in medical costs and help blunt the effects of climate change, which could save money by reducing the intensity of extreme weather events linked to a warming planet.

But the rule, much like its counterpart for new power plants, is likely to draw legal challenges from industry and conservative states once it is finalized.

The rules' opponents contend the EPA has overstepped its authority to regulate greenhouse gas emissions from stationary sources, such as power plants, and are concerned that the regulations would raise energy prices. They're also concerned the rule could force utilities to shut down too much coal-fired generation, increasing the likelihood of blackouts when demand strains the power grid.

Senate Minority Leader Mitch McConnell, R-Ky., indicated Tuesday he would push an amendment allowing Congress to block EPA power plant emissions regulations onto a bill extending unemployment insurance.

For its part, the EPA has said the rule will contain plenty of flexibility. Some stakeholders, for example, have recommended a system of credits in which generation from state renewable energy targets, investments in "smart" grid technology and energy-efficiency upgrades could be used to meet the rule's metrics.

Sensing the legal challenges ahead, the agency has been meeting with officials and industry officials around the country in an effort to ensure the rule will hold up in court.

The rule is key for meeting President Obama's goal of cutting emissions 17 percent below 2005's levels by the end of the decade. It builds on other measures aimed at curbing carbon pollution, such as new fuel-efficiency standards for vehicles and a strategy announced last week to reduce emissions from methane, a short-lived, but potent, greenhouse gas.