It's pretty similar to the blacklisting of senders. Try adding this line under smtpd_recipient_restrictions in main.cf.

check_recipient_access hash:/etc/postfix/recipient_access

Then create the blacklist file with the format of /etc/postfix/recipient_access being:

user@domain.com REJECT Dropped

another-user@anotherdomain.com REJECT Dropped

Create the hash file with: postmap hash:/etc/postfix/recipient_access

That should do it !