Carphone Warehouse has said it is investigating reports of staff acting unprofessionally at its Ecclesall Road store.
A Sheffield customer took to Twitter earlier this afternoon to enquire why the Sheffield shop was closed with the doors locked.
The customer tweeted Carphone Warehouse to report that he saw a member of staff sat at their desk when he tried to enter.
However, the member of staff then put the shutter down after the customer tried to open the locked door.
Customer, Gary Barlow, tweeted: "I wanted a quote for a repair. I went past and the doors were locked, then went down the road and came back 15 minutes later - still locked."
Carphone Warehouse replied to Mr Barlow and said they were just as curious as to why the store was closed and apologised for the inconvenience.
They said that they had escalated the customer's complaint to the regional manager to try and find out why the store was closed.
The store tweeted: "We'll investigate this with the Regional Manager, to find out why a store is shut during opening hours or acting so unprofessionally..."
The Star has contacted Carphone Warehouse for a response.