The international agreement is breached in an incident involving vampires. Legislation follows to make another such breach less likely.
There was a question about this incident on Harry’s History of Magic O.W.L. exam.
Although this is not stated, the passage of Clause 73 of the International Statute of Secrecy the very next year might be the legislation mentioned. This amendment gave the governing body of each country the responsibility for managing any magical creatures within their borders.