The Port Talbot construction company Jistcourt was meant to start building work on a £3.5m affordable housing development in Powys last Monday, but the site has been closed.
It is now understood to be going into administration.
Jistcourt is a family-run business, which was established in 1980.
The managing director, Rob Norman, told the BBC, "After a few difficult years in business, we are unable to continue trading".
The company employs 90 people at its sites in Port Talbot and Bristol.