Federal regulators announced plans Friday to dramatically limit workplace exposure to silica dust, an agent known to cause crippling lung disease and cancer in thousands of workers each year.

The proposal from the Occupational Safety and Health Administration would cut in half the amount of silica exposure allowed for general industry and maritime workers. It would slash it by 80 percent for those in the construction industry.

OSHA officials estimated the long-awaited new limits would save nearly 700 lives each year and prevent 1,600 new cases of silicosis annually for those working at construction sites, glass-manufacturing plants and other industries.

Workplace safety groups have urged OSHA for years to set new exposure limits. But the proposed rule is expected to face strong opposition from industry groups that contend lower limits are not necessary and will be too difficult and costly to measure for thousands of businesses.

It’s the first major rule proposed under new Labor Secretary Thomas Perez, who was sworn in last month.

OSHA enforces 40-year-old exposure limits for crystalline silica that the agency says are outdated, inconsistent between industries and do not adequately protect worker health.

“We know that disease occurs at exposures below the current standard,” said David Michaels, the assistant labor secretary who heads OSHA. “To truly protect the American worker, you need to lower the exposure level.”

More than 2 million U.S. workers are exposed to silica dust each year, mostly in the construction trades such as jackhammering, cutting, grinding or sawing stone, and masonry. About 200 workers die annually from silicosis, and as many as 7,300 new cases of silicosis develop each year.

Efforts to set new criteria for silica exposure have been in development for more than 15 years, and the current proposal languished for more than two years as it awaited approval at the White House Office of Management and Budget.

There will be 90 days for the public to submit comments on the rule, followed by public hearings. Michaels said he expected those hearings to last months.