The announcement by Service Employees International Union Local 521 comes nearly a week after it threatened a strike, citing issues including required overtime by emergency dispatchers.
The employees will vote on the proposed agreement Wednesday and Thursday, and union leaders are recommending that they approve it, Local 521 officials said.
"We have reached a tentative agreement!" read an announcement on the union's website.
County spokeswoman Gwen Mitchell confirmed Wednesday morning that a tentative deal had been reached and said the target time for ratifying the contract is 8 p.m. Thursday.
Local 521 also represents public health nurses, hospital assistants, tax assessors, criminalists and other county employees.
Members voted on Aug. 13 to authorize a strike, and last week threatened to have 911 emergency dispatchers join the job walk-off.
But County Executive Jeff Smith said dispatchers are essential public safety workers and that the county would request a court order to compel them to stay at work.
Votes on the tentative labor pact are set for Wednesday from 1:30 p.m. to 7:30 p.m. at Santa Clara Valley Medical Center and from noon to 8 p.m. Thursday at the County Government Center in San Jose, union officials said.