It was officially written as Zen (禪), and turned to the present character after the problems that occurred pertaining to the national script (daily-use kanji (superseded in 1981), kanji for common use (list of 1945 kanji established in 1981) and list of 1006 kanji taught in Japanese primary schools).
正しい表記は禪、国語国字問題(当用漢字、常用漢字、教育漢字)以後は現表記となる。