Some of the security guards working in buildings throughout San Francisco won't be going to work this morning.

Guards represented to by the Service Employees International Union will be on strike today.

A spokeswoman for the local chapter of the union says the strike was called because of an impasse over wages and health care benefits.

The union says the average pay for guards in the Bay Area comes to about $24,000 a year.

SEIU represents about 6,000 thousand guards working in San Francisco, Alameda and Contra Costa counties.

The union spokeswoman says the job action is the first time guards represented by the SEIU have ever gone on strike in San Francisco.