Residents in a street at "high risk" of landslips have been reminded they could be putting themselves in danger if they do not evacuate their homes.
A series of landslips on a hillside behind Ystalyfera prompted Neath Port Talbot council to order homeowners to leave their properties last week.
But some residents have said they were not prepared to leave.
Engineers fear another landslip at the rear of Cyfyng Road could cause 10 houses, numbers 81 to 96, to collapse.
"We are of the opinion that there is a high risk of further landslips and a risk to the occupiers if they remain in these properties," a council spokesman said.
"The decision to ask people to leave their homes at such short notice has not been taken lightly.
"But this is the only course of action available to the council to keep people safe."
In 2012, thousands of tonnes of rock, soil and trees slipped down the hillside behind the houses.
There have been two further landslides this year.
Council bosses have said there is no immediate solution to the issue.
"The safety of residents is our top priority and our immediate concern is for the safety of residents in the properties directly affected by two recent landslips," added the spokesman.
Officers are in contact with residents and have set up a dedicated telephone line so people "can continue to receive ongoing support".
The wider area is being assessed and monitored and the results will be known "in due course".