Princess stares out of the window of a welcome centre an hour outside Rome, watching the sky turn red. She clutches her three-month-old child tightly. The baby is all she has left after Nigeria stole her freedom, and Italy her hope.

Princess, 31, born among the muddy streets and shacks of Benin City, left everything to come to Italy in 2008. Now she is one of the thousands of women trafficked into the country who could soon find themselves on the streets, or deported back to Nigeria, under a decree that cements the populist government’s hardline immigration stance.

According to the Ministry of the Interior, approximately 40,000 Nigerian women live in Italy. Many, like Princess, have been trafficked into sex work. Most possess, or have requested, humanitarian protection. But this protection is now at risk.

According to the Institute for International Political Studies (ISPI) thinktank, in the past four months Italy has rejected more than 1,000 asylum applications submitted by Nigerian women, while an estimated 1,134 have been refused humanitarian protection.

The main element of the Salvini decree, named after the interior minister and leader of the far-right League, Matteo Salvini, is the abolition of humanitarian protection for those who are not eligible for refugee status, but cannot be deported.

After her parents died and she needed to support herself, Princess was told by traffickers that she would “find dignified work once in Italy”. The reality was very different. For five years she was forced into prostitution in various Italian cities.

She prefers not to speak about that time. The psychologists caring for her at a migrant welcome centre are aware of her ordeal and are providing counselling.

Last year, Princess sought help from an aid organisation when she found out she was pregnant. In October, she was transferred to the welcome centre in Castelnuovo di Porto, outside Rome. “I was happy,” she tells the Guardian. “I finally believed that I had found some stability. I thought I would have given birth to my child in that centre and that we would have been able to stay there, safe.”

But one month later, before formal passage of the Salvini decree, the bill was retroactively applied by the interior ministry. As a result, hundreds of migrants were evicted from welcome centres around the country. The evictions are not only affecting those whose request for protection on humanitarian grounds is pending approval, but also those in possession of permits to stay, despite the law stipulating that their status should be maintained.

The first reception centre to be evacuated was in Isola di Capo Rizzuto in Calabria.

“When the police came to tell us that we couldn’t stay there any more, I couldn’t believe my ears,” says 31-year-old Blessing, who had been trafficked from Nigeria. “They took all of our belongings and escorted us out. This is outrageous. Soon I may not have a roof over my head. I’m really frightened.”

They have always been left alone in the world, and now more than ever Isoke Aikpitanyi, founder Women of Benin City

The state police came for Princess on 23 January. She and 500 others were evicted from the refugee reception centre in Castelnuovo di Porto.

“I was hoping to finally find some peace,” she says. “And once again they asked me to move.”

Some women, like Princess, were transferred to a welcome centre managed by the Catholic church in Rocca di Papa, or to centres managed by the aid group Caritas. Dozens of others have been evicted, their whereabouts unknown.

The decree is supposed to grant victims of sex trafficking a form of protection because of the risks they may face if deported back to their countries of origin. But in order to secure protection, they must report their captor to the police or enter a rehabilitation programme.

“The majority of victims of trafficking are afraid of rebelling or of entering into psychological rehabilitation,” says Isoke Aikpitanyi, a trafficking survivor and founder of the anti-trafficking association Women of Benin City. “Until then, they are simply Nigerian women with a humanitarian permit that the authorities will not recognise. They have always been left alone in the world, and now more than ever.”

Before they leave their homes, Nigerian women are made to undergo traditional oath-taking ceremonies involving complicated and frightening rituals. The widespread use of “juju” ceremonies in trafficking women from Nigeria to Europe leaves deep emotional scars.

Escaping the sex trade: the stories of Nigerian women lured to Italy - in pictures Read more

Faith, 35, was forced into prostitution for six years on the outskirts of Milan. Wanted by the police, her abuser, or madam, fled to Nigeria. Today Faith lives in a welcome centre run by the church in Rocca di Papa, outside Rome. In a few months, a commission will decide whether to accept or deny her asylum request. She is undergoing psychological treatment, and the thought of returning to Nigeria makes her cry. “They forced me into prostitution for six years and now they could send me back to Nigeria where my madam is waiting for me, the woman who ruined my life.”

Father Enzo Volpe, a Salesian priest in Palermo, who has been providing assistance to Nigerian women for seven years, says clearing reception centres is likely to increase the risk of further trafficking and exploitation.

“Leaving these girls on the street, victims of sex trafficking, is not only inhumane, it also means facilitating the work of criminal organisations,” he says. “With no protection, these girls risk becoming easy prey.”

Names have been changed to protect identities