Did you purchase one of Apple's new 12-inch Retina MacBooks in the first few months after it launched last year? If so, you'll want to check the company's latest replacement program over the USB-C charging cables that shipped with the laptop. It seems that the cables that either shipped with the MacBook or were purchased individually through June 2015 have been determined to have a "design issue" that could cause them to stop working.
Apple's support page detailing the replacement program doesn't go into detail about the design flaw, it does say that affected USB-C cables can cause the connected MacBook to stop charging, or charge intermittently, without warning. The company notes that the cables were revised some time ago, with most customers already using the new design, meaning it's early buyers that need a replacement.
The above image details how users can identify if they have an affected cable. Early versions only have text that reads "Designed by Apple in California. Assembled in China," whereas the redesigned cables will have a serial number that follows. So if you see a serial number on your Retina MacBook's charging cable, there's no need for a replacement.
Apple says that those early MacBook customers who provided an address when purchasing or registering their computer will receive a new cable in the mail automatically, free of charge, with arrival by the end of February. Other eligible users can get a replacement by visiting an Apple Store Genius Bar or Apple Authorized Service Provider, or by contacting Apple Support directly via phone or email.