Sen. Barbara Boxer Barbara Levy BoxerThe Hill's Morning Report - Presented by Facebook - Biden, Harris launch Trump offensive in first joint appearance Bottom line Polls show big bounce to Biden ahead of Super Tuesday MORE (D-Calif.) is blocking Senate consideration of a measure to overhaul federal chemical safety rules.

Boxer, the most outspoken opponent of the bipartisan effort to reform the Toxic Substances Control Act, applied her hold on the bill Wednesday to prevent quick consideration of it shortly after Sen. Richard Burr Richard Mauze BurrRep. Mark Walker says he's been contacted about Liberty University vacancy Overnight Defense: Trump rejects major cut to military health care | Senate report says Trump campaign's Russia contacts posed 'grave' threat Senate report describes closer ties between 2016 Trump campaign, Russia MORE (R-N.C.) agreed to lift a hold he had kept in place for over two months.

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Sen. James Inhofe (R-Okla.), chairman of the Environment and Public Works Committee, accused Boxer of going back on her pledge to him to allow the legislation to move through consideration.

“It’s simply something that really bothers me because you’re breaking a commitment that you made,” Inhofe told reporters.

“She’s reneged on her commitment,” he said.

Inhofe is hoping to get the bill passed before the end of the week, when senators are scheduled to go home and end the year’s session.

Boxer’s office did not respond to requests for comment.

She has fought tooth and nail against the Frank R. Lautenberg Chemical Safety for the 21st Century Act, named after the late senator and now sponsored mainly by Sens. David Vitter (R-La.) and Tom Udall (D-N.M.).

While it has dozens of co-sponsors in both parties, Boxer argues the chemical bill would be a significant step back for safety that would reduce states’ authority to regulate substances and make it difficult for regulators to act on high cancer rates, among other problems.

“This is the environment committee, not the boardroom of the chemical companies,” she said when the committee passed the bill earlier this year.

Burr had placed a hold on the bill to demand that the Senate consider renewing the Land and Water Conservation Fund (LWCF).

The government spending bill released early Wednesday would provide a three-year renewal of the LWCF, spurring Burr to drop his hold.

The LWCF, which enjoys bipartisan support, expired Sept. 30.

Devin Henry contributed to this story.