Hard-line Hindu groups threatened on Tuesday to blacken the faces of couples celebrating Valentine's Day, saying the Christian saint's day was a violation of Indian culture.
Valentine's Day, which falls on Saturday, has steadily gained popularity in India in recent years, but Hindu hard-liners, incensed by what they see as creeping westernisation, have often disrupted celebrations and stormed shops that sell greeting-cards in protest.
"The heads of those not adhering to our requests would be shaved. Their faces may also be blackened," said Dilip Khandelwal, a leader of the Vishwa Hindu Parishad (VHP) group in the central state of Madhya Pradesh.
"We will not allow any such foreign festival, which is a violation of Indian culture, to be celebrated in our land."
Police said they would tighten security for the day, which has been marked by violence in some parts of India in the past.
"We will maintain a strict vigil and also keep an eye on those found teasing in the name of Valentine's Day," said Vipin Maheshwari, a police superintendent in Bhopal, the capital of Madhya Pradesh.
Two years ago, Bal Thackeray, firebrand leader of the ultra nationalist Shiv Sena, called for a ban of the celebrations on February 14.
Hard-line Hindus from the Shiv Sena, the VHP, and an allied group, the Bajrang Dal, who say the celebration offends Indian social values, have invaded gift shops, burned cards and disrupted celebrations in many parts of India in the past.
But people in cities such as New Delhi and Bombay are unfazed.
Shop windows are decorated with heart-shaped balloons, cards, gifts and paper roses in the run up to Valentine's Day, while advertisements fill radio and newspapers.