Members of a gang who forced Vietnamese girls and women into slavery in nail bars in Britain have been jailed for a total of nine years in what police believe is the first case of its kind.

Giang Huong Tran, 23, Viet Hoang Nguyen, 30, and Thu Huong Nguyen, 49, were sentenced on Tuesday after being convicted of human trafficking and modern slavery offences.

Police said the “sophisticated money-making operation” involved the exploitation of vulnerable Vietnamese teenagers who were physically and verbally abused.

“The victims worked for no money and were trafficked between nail bars according to demand,” Senior Crown Prosecutor Eran Cutliffe said in a statement. 

“They were hidden from the authorities in order to avoid detection whilst being exploited in plain sight within our society.”

The defendants were caught after police traced a missing Vietnamese teenager to a nail bar in Burton-on-Trent in central England, Stafford Crown Court heard.

The shop’s owner Viet Hoang Nguyen, known as Ken, was sentenced to four years, while manager Tran, known as Susan, received a suspended two-year sentence.

Thu Huong Nguyen, known as Jenny, who owned a nail bar in the historic western city of Bath, was sentenced to five years. Police said 60,000 pounds ($81,500) in cash was discovered concealed in a stuffed toy at her home.

Nguyen and Nguyen were convicted of facilitating the trafficking of victims to work in nail bars. Tran was found guilty on a forced labor charge.

Britain’s Vietnamese community has set up nail bars across the country but experts say traffickers have piggy-backed off their success.

Vietnam consistently ranks as one of the top three source countries for potential victims of modern slavery in Britain.

Britain’s anti-slavery commissioner Kevin Hyland has called for tighter regulation of nail bars and said a government estimate that there are 13,000 victims of forced labor, sexual exploitation and domestic servitude in the UK is just the tip of the iceberg.

Detective Inspector Clair Langley, of Staffordshire Police, said the speed with which the victims were moved around the country indicated a high level of organization.

“This is the first successful prosecution for child labor exploitation and child trafficking under the Modern Slavery Act and we hope it sends out a clear message – we won’t tolerate this activity and we will bring offenders before the courts.”

The Modern Slavery Act of 2015 introduced life sentences for traffickers, offered better protection for people at risk of being enslaved, and forced companies to check their supply chains for forced labor.

Detective Inspector Charlotte Tucker, who led part of the operation, said the case was “desperately sad”.

“As a community we need to look out for the warning signs and do our part to stop this archaic practice once and for all,” she said.