The Apple operating system, OS X, is setup by default to use the US Letter format under the "Print & Scan" settings page (you can find this page under "System Preferences"). If you are running into issues printing labels, this could be one reason.
To resolve this issue, follow the steps below.
Note: Mac OS X 10.6 and earlier will not let you set a custom default print size.
Navigate to the File menu to find Page Setup.
Select "Format For" and then click "Any Printer."
Choose the correct paper size.
If printing any size besides "Letter" you'll need to add a custom paper size. If you are printing to a "Letter" size, skip to the step for "Find the label you want to print.".
Select “Manage custom sizes” at the bottom of the Paper Size menu.
Change the name by single clicking on "Untitled". We recommend changing the name to something you will remember, such as "4x6".
Set the Paper Size to the correct width and height. For example, width: 4 inches; height: 6 inches.
Leave the "Non-Printable Area" set to "User Defined" and change the margins if necessary - we suggest a very small margin or no margin.
Click "OK" on the "Custom Paper Sizes" page to save your changes.
Click "OK" on the "Page Setup" page.
Find the label you want to print. Press Command + P
Make sure “Ignore Scaling” and “Shrink To Fit Page Width” is checked.
Press "Print".