The Waxman-Markey climate-change bill could add as much as $1 billion to production costs for U.S. steelmakers by 2030, according to a report by Goldman Sachs Group Inc., equivalent to an increase of $10 to $12 per ton.

That finding backs the contentions of steel producers who stand in strong opposition to the cap-and-trade provision to reduce carbon emissions, which was passed by the House of Representatives and now is headed to the Senate for a vote expected later this year.

Goldman Sachs' report, released Thursday, said that costs added to the domestic steel industry through provisions in the bill would reduce the ability of U.S. mills to be competitive in global markets unless imports were equally penalized.

"As costs of...