Initially, there was a vote in parliament to allow it, because at the time they were holding temporary ID cards. In the past, holders of these temporary ID cards were allowed to vote, because they were considered by the government as not really being stateless, but as being doubtful citizens that need to be verified. So during all of the past elections in the 1950s, 1960s, and even in the 1990s, the Rohingya have been allowed to vote. However, just before the election in 2015, there was a discussion about organizing a constitutional amendment referendum, and the law for that included temporary cards.
Suddenly, the Rakhine, especially the monks, started leading protests and demonstrations throughout the country, saying they would use violence if the government did not stop the Rohingya from voting. Of course, the next day, on February 11 of last year, then president Thein Sein, suddenly announced that from then on, the white cards, the temporary ID cards, were cancelled. So now the Rohingya cannot vote because they have no ID cards.