code: public function getPackageLabels($request)
      {
          if (!($request instanceof FBAInboundServiceMWS_Model_GetPackageLabelsRequest)) {
              $request = new FBAInboundServiceMWS_Model_GetPackageLabelsRequest($request);
          }
          $parameters = $request->toQueryParameterArray();
          $parameters['Action'] = 'GetPackageLabels';
          $httpResponse = $this->_invoke($parameters);
  
          $response = FBAInboundServiceMWS_Model_GetPackageLabelsResponse::fromXML($httpResponse['ResponseBody']);
          $response->setResponseHeaderMetadata($httpResponse['ResponseHeaderMetadata']);
          return $response;
      }
docs: Get Package Labels
  Retrieves the PDF-formatted package label data for the packages of the
  shipment. These labels will include relevant data for shipments utilizing
  Amazon-partnered carriers. The PDF data will be ZIP'd and then it will be encoded as a Base64 string, and
  MD5 hash is included with the response to validate the label data which will be encoded as Base64.
  The language of the address and FC prep instructions sections of the labels are
  determined by the marketplace in which the request is being made and the marketplace of
  the destination FC, respectively.
  
  Only select PageTypes are supported in each marketplace. By marketplace, the
  supported types are:
  * US non-partnered UPS: PackageLabel_Letter_6
  * US partnered-UPS: PackageLabel_Letter_2
  * GB, DE, FR, IT, ES: PackageLabel_A4_4, PackageLabel_Plain_Paper
  * Partnered EU: ? <!-- TODO: define this -->
  * JP/CN: PackageLabel_Plain_Paper
  
  @param mixed $request array of parameters for FBAInboundServiceMWS_Model_GetPackageLabels request or FBAInboundServiceMWS_Model_GetPackageLabels object itself
  @see FBAInboundServiceMWS_Model_GetPackageLabelsRequest
  @return FBAInboundServiceMWS_Model_GetPackageLabelsResponse
  
  @throws FBAInboundServiceMWS_Exception