email notifications via paster plugin post erroneously demands authentication

When calling

echo '{}' | /usr/lib/ckan/default/bin/paster --plugin=ckan post -c /etc/ckan/default.ini /api/action/send_email_notifications

the following error is returned:

Error - <type 'exceptions.Exception'>: Action function
send_email_notifications did not call its auth function
     <html>
     <head>
     <title>Server Error</title>
     </head>
     <body>
     <h1>Server Error</h1>
     An internal server error occurred
     </body>
     </html>

However, when called using curl, auth-key set in header and empty json {}, the action succeeds.