Not officially banned, but there have been Russification policies in Latvia under Russian occupation since 19th century. During Soviet occupation after WWII lots of organized colonization by Russian speakers happened (Latvians were 75% in Latvia in 1935, 52% in 1989, now it's 62%; in comparision - 10%, 34%, 27% for Russians). It was often that you couldn't speak Latvian in a shop or workplace. It's still happening actually, but not so widespread.