WASHINGTON — For federal contractors, it's time to start checking whether employees are able to legally work in the United States.

Beginning today, the federal government is requiring federal contractors to use the E-Verify system to check the immigration and citizenship status of the people they hire and assign to new federal contracts.

Contractors have 30 days from the date a contract is awarded to enroll in E-Verify, and 90 days to start submitting information on new hires and certain current workers. Contractors have the option of checking their entire work force, once they notify the government of their intent to do so. They also will be responsible for requiring subcontractors to use E-Verify.

As the rule takes effect and more workers' information goes through the system, there is likely to be a spike in the number of workers who are not confirmed as permitted to work in the U.S., said Cynthia Lange, a partner of Fragomen law firm, who is based in California.