Two sweeping environmental laws have given the Environmental Protection Agency power to influence policy at every level of government, raising concerns the agency has crossed the line separating the executive branch from the legislative branch.

The National Environmental Policy Act and the Clean Air Act require the EPA to comment on environmental impact statements, which every agency files for proposed legislation or projects with an environmental component.

Each agency comments on EISes under their jurisdiction, but under the policy governing the environmental review process, the EPA has the ability to follow up on mitigations and, if it finds proposed solutions insufficient, to involve the president.

"It's by far the most powerful regulatory agency in country," said Bonner Cohen, a senior fellow with the National Center for Public Policy Research, told the Washington Examiner.

The EPA resolves "unsatisfactory proposals" by consulting with other agencies, including the White House Council on Environmental Quality, according to the environmental review policy. The CEQ chairman is also President Obama's top environmental policy adviser.

"It's a subtle way for EPA to expand its regulatory empire without issuing another regulation," Cohen said.

In doing so, it has crossed the line from executive agency to legislative, he said.

About 75 percent of the EPA's comments were incorporated into agencies' final EISes in 2012, according to a recent EPA inspector general's report.

Anyone may comment on an EIS, but environmental review policy gives only the EPA the ability to follow up on mitigations the lead agency agrees on, according to the IG.

Other agencies also comment on projects under their jurisdiction, but the EPA is aggressive about its environmental oversight, said a spokesman for the Federal Highway Administration, which has filed more than 30 EISes so far this year.

The EPA uses its authority over environmental issues to implement its energy agenda without going through the legislative process, according to Louisiana Republican Rep. Bill Cassidy.

"The EPA is dictating energy policy, not the Department of Energy, not Congress," Cassidy said.

The EPA enacts its agenda by legislating through burdensome regulations, Cassidy said. The EPA last week unveiled its new rules for coal plants, which make it economically unfeasible to open a new coal plant.

The agency is prejudicing electrical generation toward solar and wind despite their expense, simply by the regulations they issue, he said.

"It's clear that the EPA, officially and unofficially, has a great deal of influence on our economy," Cassidy said.

The EPA has more regulatory actions under review by the White House Office of Management and Budget than any other agency, according to an April study by the House Energy and Commerce Committee, which Cassidy sits on. Some of its most expensive rules are also its most recent.

The Utility MACT rule governing coal plant emissions, which go into effect in 2015, is estimated by the agency itself to cost $9.6 billion per year for several decades, and an independent analysis estimates total compliance costs will reach more than $100 billion, according to the committee report.

The Boiler MACT rule, which governs industrial and commercial boilers and heaters, is estimated to cost as much as $1.6 billion each year.

Cassidy summarized his concern with the EPA's costly regulatory agenda by paraphrasing 19th-century Supreme Court Chief Justice John Marshall: "The power to tax and the power to regulate is the power to destroy."