The group were said to have been based in Praia da Luz when the three-year-old disappeared from a holiday complex in 2007.
It has been reported one property owner claims detectives investigating her disappearance asked four times about the cleaners working in Portugal.
It is understood the officers became aware of the six to eight British workers – said to have used a white van – after going over evidence from the original Portuguese investigation.
Now, detectives are asking owners whose properties overlook the flat where Madeleine stayed for information about the group.
It is the first time the cleaners have been mentioned during any investigations into the then three-year old's disappearance.
A Met Police spokesman said speaking to individuals was part of its review of the case.
He added: "This is routine procedure as part of the ongoing review."
Kate and Gerry McCann, of Leicestershire, have campaigned tirelessly to trace their daughter.
Mr McCann, who is originally from Glasgow, battled for the Metropolitan Police review, which began 18 months ago.