Six potential victims were rescued and safeguarded during the operation by the Gangmasters and Labour Abuse Authority (GLAA) supported by officers from the Metropolitan Police.
Two addresses in the Newham and Barking areas were targeted yesterday morning.
The suspect, a 24-year-old Romanian man, has been interviewed and released under investigation pending further enquiries.
All six potential victims are Romanian men in their 20s.
The GLAA acted after it received intelligence that the potential victims had been trafficked to the UK for financial exploitation while working in construction.
GLAA Senior Investigating Officer Tony Byrne said: “While we are in the early stages of the investigation, I am very pleased that we have already been able to help six potential modern slavery victims who are now getting the expert support that they need.
“We are grateful for the assistance provided by our colleagues in the police.
“Once again, this demonstrates the importance of positive partnership working to protect vulnerable and exploited individuals.”