Uruguay is a signatory to the Single Convention on Narcotic Drugs which requires that all signatories criminalize the manufacturing and possession of drugs, including marijuana. However Uruguay has taken steps to legalize the drug back in 2012 and the liberal law is coming into full effect this year. Despite that, the United Nations hasn't reacted to the new law and hasn't tried to punish Uruguay.
Why isn't Uruguay facing any penalties from the UN? A similar question could apply towards Canada once they legalize cannabis as well.