SAN DIEGO (CNS) - Certain Metropolitan Transit System bus routes in San Diego was interrupted for a third day Friday as striking drivers continue to walk the picket lines.

Unionized drivers -- members of Teamsters Local 542 -- began striking Wednesday after contract negotiations with their employer, First Transit, reached a standstill. First Transit supplies drivers for paratransit vehicles and 18 of the 95 MTS bus routes, according to the company.

RELATED LINK: Service Disruption - MTS Access and some Fixed Routes

Affected MTS Access service and bus routes include 14, 18, 83, 84, 88, 851, 870, 944, 946, 965, 972, 973, 978 and 979. Routes 25, 833, 945 and 964 were operating with limited service, according to MTS.

MTS Access drivers provide 1,900 daily curb-to-curb trips that get people to hospitals, doctor appointments and regional care centers. The bus routes are generally served by mini-buses and carry around 4,300 passengers a day.

RELATED: Union representing MTS bus drivers votes to strike

Major bus routes and the trolley were not affected by the work stoppage, according to MTS. However, Access paratransit in the North County was halted due to the strike, as was the Sorrento Valley Coaster Connection bus shuttle service, according to the North County Transit District.

MTS Access riders and riders of affected fixed route services were encouraged to make alternate transportation arrangements by calling (888) 517- 9627 or (800) 921-9664. Those who usually use services in the North County were asked to call (760) 726-1111.