Which vehicle may be operated in the path of the taxiing aircraft?

At a controlled airport any vehicle (another plane, car, fuel truck, snow plow, mower, or even a unicycle) may be operated in the path of a taxing aircraft, but they must have a clearance to do so from ground control. At an uncontrolled airport the aircraft should have the right of way but so does a pedestrian at a cross walk, so use your head.