An A319 crew reported low yellow hydraulic quantity during preflight at an out station but maintenance would not get contract maintenance so after engine start and taxi the crew returned to the gate because both the yellow and green system reservoirs were low.

Narrative

At the gate; prior to push. During cockpit crew preflight of aircraft. The Yellow Hydraulic system was below the acceptable level for dispatch (qty was below the 'box'). Captain called Dispatch/tech desk on HIS phone and informed them we needed to have the Yellow Hydraulic system serviced. The said NO; they didn't want to call out contract maintenance and that it would be at an acceptable level after cargo door closure and engine start. The Captain disagreed and stated that he wanted it serviced and to check the Green quantity as it was at the lower level of acceptance. The response was still; take the aircraft and it will be OK. Captain said OK; however after engine start; if any were low we would return to the gate. After pushback and engine start; BOTH Green and Yellow Hydraulic quantities were below the 'box'; meaning outside the parameters for acceptable dispatch; and we returned to the gate and Contract Maintenance was called out. It took 30 minutes to service the Hydraulics and continue. The actual hydraulic quantities were recorded on the Captain's cell phone camera. Another note. NO ONE checked the aircraft on the overnight; meaning no mechanic checked it over for an airworthy condition; or this would have been discovered; OR they were not doing their job! Common sense will provide that answer; provided the airline cares enough to make a change.