City spokeswoman Anne McGrath says the spill occurred around 9 a.m. Monday in the laundry room of the Portola Hotel in downtown Monterey.
The spill apparently occurred when chlorine mixed with other chemicals in the laundry room. City officials are still investigating.
McGrath says more than two dozen people complained about respiratory problems.
The Monterey Herald (http://bit.ly/yb9Dm8 ) reports that 16 workers and one guest went to a hospital.
The hotel has been cleaned and decontaminated. It was expected to reopen Monday afternoon.