Unionized workers at the northern Chilean port of Antofagasta are currently on strike and copper shipments at the port have been held up, a port spokeswoman said Thursday.

Although several mining companies ship their copper out of Antofagasta, most tend to divert their shipments to other nearby ports, such as Mejillones, in the event of strikes, a person familiar with port operations said.

"The port is closed and there's copper that's waiting at the docks, but there are no ships in the harbor waiting to load right now," the spokeswoman for Antofagasta Terminal Internacional, or ATI, told Dow Jones. She added she couldn't identify the mining company or companies whose copper was held up by the strike.

State copper giant Corporacion Nacional del Cobre, or Codelco, mostly ships its copper out of Mejillones, and the BHP Billiton Ltd. (BHP)-controlled and operated Escondida mine ships its copper concentrates out of its own port, Puerto Coloso.

Union leaders and management are scheduled to meet later Thursday in the hopes of reaching an agreement.

Workers originally sought a 4 million Chilean peso ($7,222) end-of-conflict bonus but reduced their demand to a CLP1.5 million bonus, a union leader told the CNN Chile television network. Union leaders couldn't immediately be reached for comment.

-By Carolina Pica, Dow Jones Newswires; 56-2-820-4244; carolina.pica@dowjones.com