In order to minimize paper handling problems labels should be printed using the optional media feeder which attaches to the manual feed slot. The media feeder helps prevent skewing, and also provides a straight-through paper path for the labels as long as the face-up tray is also installed. Using the paper trays or choosing face-down printing increases the risk that a label might come unglued from the backing sheet and cause a paper jam.
The adhesives used in the labels should be able to withstand a temperature of approximately 410 degrees fahrenheit for 0.1 seconds. The fuser temperature during standby is 392 degrees fahrenheit (200 degrees Celsius) and rises to 410 degrees fahrenheit (210 degrees Celsius) when printing. These values are slightly higher than 8 ppm print engines because the fusing process must occur in a shorter period of time at 20 ppm. These are the default fusing temperature values as shipped from Apple, but they can be modified slightly by changing the parameters while in the service mode.
Label sheets that have missing labels, or that have any part of the backing sheet exposed should not be used. Labels that have areas of exposed adhesive should also not be used because the adhesive will adhere to the rollers and components in the paper path.
There are several manufacturers who are marketing special labels for the laser printer market. Apple suggests consulting with your local paper supplier or computer store for more specific information.