Priyanka Tamaychekar's marriage hasn't been arranged yet, but already the 26-year-old is dreading her wedding night.

Key points: Wedding night virginity testing is practised by the Kanjarbhat ethnic group of India

Wedding night virginity testing is practised by the Kanjarbhat ethnic group of India Brides who 'fail' can be subjected to beatings, humiliation and divorce

Brides who 'fail' can be subjected to beatings, humiliation and divorce Opponents campaigning to end the practice have faced violence and threats

In her first few hours as a newlywed, Priyanka will be expected to submit herself to a humiliating ritual, just as brides in her family have done for centuries.

"The bridegroom will go inside with a white bedsheet and he has to come out with a red bloodstain on it," she said.

"People outside are sitting, waiting, and they will ask him if the 'product' was good or not good."

The "product" is her, the bride.

And if she doesn't bleed on her wedding night, she can be subjected to beatings and communal humiliation — even a divorce.

Wedding night virginity testing is practised by the Kanjarbhat ethnic group of India at the behest of tribal elders.

Members of a caste council — all-male, unelected — oversee the ritual and mete out repercussions if the bride "fails" the test.

Refusing to participate can make you an outcast among your own friends and family.

Opponents of virginity testing are reaching out to other like-minded people through WhatsApp and Facebook. ( ABC News: Siobhan Heanue )

Priyanka is among a group of young women and men from within the community who are railing against the practice.

She plans to refuse to take part.

Vivek Tamaichikar, 28, is due to be married next month.

He has refused to subject his wife-to-be to the ritual, which he calls humiliating and a violation.

His mother threatened to throw him out of the house and cancel his marriage if he refused to follow tradition.

The group opposed to virginity testing meet at a house to discuss strategy. ( ABC News: Siobhan Heanue )

But he started a WhatsApp group and a Facebook collective to gather like-minded members of the community and launch a campaign to end the practice.

One of them is Priyanka, who was relieved to find other people within her community who thought the same way as her.

"I used to think that I'm the only girl thinking about this ritual and I did not like this because it is against a woman's dignity," she said.

The group of youngsters is based in Pune, in the western state of Maharashtra, where large numbers of the Kanjarbhat ethnic group have migrated from northern India.

Elders push 'demonstrations' and porn on newlyweds

Vivek Tamaichikar has refused to subject his wife-to-be to the ritual. ( ABC News: Siobhan Heanue )

Vivek says the ritual violates both the bride and the groom's privacy.

The groom is given a white cloth to use while having sex with his bride on their wedding night.

Elders sit outside the door of the couple's room until the act is complete.

Before the couple enters, the elders sweep the room for any sharp objects that may be used to produce blood.

The bride's bangles are removed so that she can't cut her skin with them.

And there's a time limit.

"Every five to 10 minutes they will keep on knocking and they will keep on asking if you are done with the intercourse," Priyanka said.

If nothing happens, the elders will go in and encourage the couple to watch porn or instruct them on how to have intercourse.

The process ignores medical evidence that a woman's hymen can be ruptured without sexual intercourse. ( ABC News: Siobhan Heanue )

"They keep offering help to instigate sexual activity, like blue videos or medicines," Vivek said.

"In case the couple is not in the mindset, or they are not able to go through intercourse, they will even demonstrate to them with a real couple.

"They will send a couple inside and they will do the physical act in front of them, they will show them porn videos.

"They will do anything to pressure them, but they have to pass this test."

After sex, the groom is expected to display the white bedsheet for inspection by relatives and elders.

"He's supposed to tell the whole caste council consisting of 150, 200 people that, my 'product' was perfect, my 'product' was pure," Vivek said.

If the bride is deemed "impure", there are several possible outcomes.

She is often pressured tell the community elders who she has had sex with.

The process gives no credit to medical evidence that a woman's hymen can be ruptured without sexual intercourse, and that not all women bleed when it is broken.

Unelected caste councils were banned in the state of Maharashtra last year, but they still exist. ( ABC News: Siobhan Heanue )

According to caste traditions, a bride deemed to be impure can be beaten, her family can be fined, or the marriage can be annulled.

A woman who "fails" the test is seen as bringing shame to her family, and there are cases of brides being locked up in their parents' house as punishment.

No ritual exists to test the groom's virginity.

Violence, threats for opposing ritual

Taking a stand against tradition hasn't come without consequences for the members of the group.

Three of them said they were bashed by about 40 people at a community wedding earlier this year.

The group often uses social media to gather support — but they have also faced violent opposition. ( ABC News: Siobhan Heanue )

Some of them have had their cars and motorbikes vandalised. Most have been threatened by their own family members.

Vivek said his first encounter with the ritual and its ramifications was at the wedding of a female relative.

He was still a child when he witnessed the bride being beaten by her own mother the morning after the wedding festivities, because she had failed the virginity test.

"That was very confusing and surprising for me to see," he said.

"We've all been pressured to leave the group," said Priyanka, whose own grandfather is a member of the caste council.

But she said she'll keep raising her voice.

"Oh my gosh, in India and in 2018 these rituals are still going on," she said.

The men and women who have joined forces to protest the purity test are mostly university students.

They've been privy to a level of education that their parents never received.

Wedding night virginity testing is practised by the Kanjarbhat ethnic group of India. ( ABC News: Siobhan Heanue )

Indian law is also more progressive on the issue.

Unelected caste councils were banned in the state of Maharashtra last year, but they still exist, often wielding influence over local officials.

They threaten social exclusion to community members who oppose them, which means an outcast can't attend community events or find a marriage partner.

Priyanka said she's willing to risk ostracism and conflict within her family to preserve her own dignity.

"I have anger that is developing in my heart," she said.

"Why does this happen only to a girl and not a boy, not a man?

"I have to do something," she said.

For Priyanka, doing something means not doing what women in her family have been told to do for generations.