Hundreds of janitors at 20 buildings on L.A.’s Westside were set to walk off the job Wednesday night after contract talks with building owners broke off earlier in the day.

The walkout comes after janitors voted to authorize a strike around noon on Wednesday, according to Service Employees International Union Local 1877 President Mike Garcia.

The contract between SEIU Local 1877 and building owners expired on April 30, but was extended last week until Wednesday to allow for more negotiations.

Garcia said the talks broke down over the issue of a two-tier pay and benefits system, which provide higher pay and benefits to janitors at buildings in Downtown Los Angeles and Century City than buildings elsewhere on the Westside.

“The maintenance companies have offered a package with unprecedented improvements in wages, health and pension benefits,” Dick Davis, chief negotiator for the L.A. Maintenance Contractors, said in a statement released Thursday. “We are more than disappointed that the union rejected such a substantial package and would urge them to re-consider, but we will work steadfastly to negotiate a contract in the mutual best interest of workers, tenants, building owners and managers and the public. In the meantime, we fully intend to service our customers during any work stoppage.”

The building maintenance companies involved in the bargaining include: Able; ABM Janitorial Services; DMS; IFS; Merchants; One Source; Universal; Peerless; Servicon; NBS; Advance; UPM; and Columbia.

Garcia said that Los Angeles Mayor Antonio Villaraigosa has called representatives of the two sides into his office Thursday afternoon to try to arrange a cooling off period to give more time to reach a deal. Villaraigosa brokered a settlement between Downtown building owners and security guards in June 2005, just before he took office.