Union Urban Development Minister Venkaiah Naidu on Wednesday said chanting of 'Om' during yoga sessions on the International Yoga Day on June 21 is not mandatory."Do not make yoga controversial. ‘Om’ is not mandatory. Yoga is a great ancient Indian art which will discipline both the body and the mind," said Naidu in a tweet.Naidu's comments come after reports about a central government circular that proposed chanting of 'Om' and recitation of Vedic mantras before the 45-minute yoga session on June 21.Earlier, the AYUSH (ayurveda, yoga, unani, siddha and homeopathy) ministry too said no attempt be made to create a controversy over the International Yoga Day, as no one will be compelled to chant 'Om'."There is no compulsion to chant 'Om' before the yoga session. It is completely voluntary and one can remain silent. No one will object," AYUSH ministry joint secretary Anil Kumar Ganeriwala had told IANS.