Union Bank of India (UBI) today said that its follow-on public issue will open on February 15.The issue, comprising 4.5 crore equity share of Rs 10 each for cash at a premium to be decided through the book building process, would remain open for subscription till February 21.UBI, CMD, K Cherian Varghese said the price band for the issue would be announced on February 14.Post-issue, government's stake in the bank would come down to 55.43% from 60.85% now.