The Spar shop and filling station on the Armagh Road, Portadown, is set to close on Christmas Eve.
The staff, who number around 15, were told last Friday.
They are awaiting details on whether they will be relocated within the Henderson-owned company.
A worker told the Portadown Times that as far as he was aware “the company is taking care of the staff”.
The shop, on the corner of the Armagh Road and Brownstown Road, is currently ‘running down’ stock in preparation for the closure.
It is believed Henderson’s will be concentrating on the former P&G store, which they recently took over, and which is at the other end of the Brownstown Road.
The Portadown Times is awaiting a formal response from the Henderson group.