Coal-fired power plants would be eligible for billions of dollars in extra tax breaks under U.S. President Joe Biden’s economic legislation if they install carbon-capture systems, an incentive that environmental groups say may delay the retirement of dozens of facilities.

Power plants that capture their carbon dioxide emissions would be eligible for a tax credit of as much as $85 per metric ton under the draft of Biden’s $1.75 trillion spending plan released by the House last week. That’s an increase from a rate of $50 a metric ton in current law.

The change could result in a single 1,000 megawatt coal plant receiving $6 billion in payments over 12 years, according to an analysis of the proposed credit by the environmental group Sierra Club, which estimates the increase could result in a quarter of the nation’s coal-fleet delaying retirement.