JEFFERSON CITY, Mo.—Missouri Gov. Jay Nixon on Friday vetoed legislation that aimed to make workers compensation the exclusive remedy for most occupational diseases and limit employee liability for workplace accidents.

Missouri's S.B. 572 would have required occupational diseases to be covered solely by workers comp, except in cases of toxic exposure to chemicals, radiation and other substances caused by a third party.

A separate clause said that an employee's co-workers can't be sued for workplace injuries or deaths that would be covered by workers comp, excluding cases of negligence.

In a letter to the Missouri Legislature on Friday, Gov. Nixon said the exclusive remedy provision could block workers from seeking compensation for mesothelioma and other diseases that “involve long-term workplace exposure to toxic substances.”

“Current law appropriately recognizes the severity and duration of these types of occupational diseases, which may take years or even decades to manifest themselves, by allowing affected workers broader redress through access to the civil justice system,” the letter reads. “Taking this right away from workers suffering from serious and deadly occupational diseases... is not acceptable.”

The governor disagreed with the liability provision because he said it could hinder a “timely and efficient” claims process.

“It is questionable whether holding a civil action in abeyance pending “exhaustion” of all ‘administrative remedies'—terms that, moreover, are not defined in the bill—furthers these goals,” the letter reads. “Procedural requirements should foster an efficient and equitable resolution for all parties.”

In a statement Friday, the Missouri Chamber of Commerce and Industry said it was “disappointed” in Gov. Nixon's decision to nix S.B. 572. The Jefferson City, Mo.-based group said the bill would have closed loopholes that were created in a 2005 reform of Missouri's workers comp law.

“It was never the intent of lawmakers to exclude these situations from the law when reforms were enacted in 2005,” said Daniel Mehan, chamber president and CEO, in the statement. “These provisions would have returned the law to the way the system has operated for decades.”