You can read more about May 31th: 1st anniversary of Gezi Park events here. Like last year, the public transportation going to/from Taksim, especially the Taksim metro line does't operate. The stops Şişhane, Taksim and Osmanbey have been closed since 9:00 am today and will be clodes until the further notice.
For more news and information about the Consequences of the Gezi park protests, please click on the link. Here you can find some additional information about the protest, which took place in late May and June 2013, itself.
Lets hope that this anniversary will pass in a more pacific way.