The Muggle Protection Act was a proposed Ministry of Magic by law that was presumably designed to protect Muggles from potentially harmful magical artefacts. According to Lucius Malfoy, it was partially written by Arthur Weasley, the head of the Misuse of Muggle Artefacts Office, and resulted in the Ministry conducting searches for Dark objects, including those located at Malfoy Manor.
Some pure-bloods found the proposed legislation offensive, presumably because they were prejudiced against Muggles and did not want the Ministry searching their possessions. Lucius Malfoy went so far as to try to sabotage Arthur's career by planting an old diary of Tom Riddle's on Arthur's daughter, which led to the opening of the Chamber of Secrets and the petrification of several Muggle-born students. This law was passed in 1992, despite opposition from Lucius Malfoy.