An employee works on a Telsa Motors Model S sedan as it makes its way along an assembly line at company's assembly plant in Fremont, California.

California's Occupational Safety and Health Administration started an investigation into Tesla on Tuesday, according to a spokesperson for the agency.

The investigation followed a report by Reveal on Sunday alleging that Tesla under-counted and mis-labeled employee injuries at its electric vehicle factory in Fremont, California, as well as a paint shop fire that occurred there in early April. Tesla has disputed the report by Reveal and characterized the fire as "small."

"Cal/OSHA takes seriously reports of workplace hazards and allegations of employers' underreporting recordable work-related injuries and illnesses," the agency said in a statement.

Cal/OSHA's inspections of the Tesla Fremont factory will, among other things, determine whether the electric car company is reporting serious injuries directly to the agency within eight hours, as required by law.

Such investigations typically take 3 to 6 months. The agency is likely to conduct multiple on-site visits to Tesla's Fremont factory as part of the probe, but does not provide detailed information on open investigations.

Cal/OSHA defines a serious injury or illness as one in which an employee is hospitalized for more than 24 hours or when a part of the body is lost or permanently disfigured.

Read CAL/OSHA's statement:

Cal/OSHA takes seriously reports of workplace hazards and allegations of employers' underreporting recordable work-related injuries and illnesses on the Log 300. Cal/OSHA currently has an open inspection at Tesla.While we do not disclose details of open inspections, Cal/OSHA's inspections typically include a review of the employer's Log 300, as well as a review to ensure that serious injuries are reported directly to Cal/OSHA within eight hours as required by law. Cal/OSHA's regulations define a serious injury or illness as one that requires employee hospitalization for more than 24 hours for other than medical observation, or in which a part of the body is lost or permanent disfigurement occurs.

Tesla issued this statement in response:

"The injury rate at our Fremont factory is half what it was in the final years of the UAW plant operated by GM/Toyota immediately before us, and we care deeply about the safety and well-being of our people and strive to do better every day. Cal-OSHA is required to investigate any claims that are made, regardless of whether they have merit or are baseless (as we believe these are), and we always provide our full cooperation. Last year, a Cal-OSHA investigation into our injury reporting and record-keeping was closed without any violations found and without any further action taken. In fact, unlike other automakers who in the past have been cited by OSHA for record-keeping violations, we have never in the entire history of our company received a violation for inaccurate or incomplete injury record-keeping."

-- Lora Kolodny and Phil LeBeau contributed to this report.