Businesses have warned that they face potential ruin with the emergency closure of part of the A5, one of north Wales' most important roads.
The section of the A5 will be shut from the bank holiday weekend
The 1km stretch between Ty Nant in Denbighshire and Dinmael in Conwy could be shut for several months from 26 May because of an unstable rock face.
Some small businesses are worried the lack of passing trade will mean huge losses during the tourist season.
The assembly government apologised, but said safety was a priority.
The A5 trunk road leads past Llangollen in Denbighshire to Holyhead on Anglesey through the Snowdonia National Park, and is used by thousands of tourists every day during the summer months.
The road is being closed from 2100 BST next Friday, before the bank holiday weekend.
Local traders are concerned that delays and diversions could discourage tourists from visiting towns across the region.
Philip Hughes, estate manager at Rhug Estate in Corwen, said passing trade was "absolutely essential".
He said: "Our turnover doubles in the summer with the tourist trade coming through.
"The small closure of the A5 just west of us will potentially be very damaging, unless the message can be got across that there is a very small local detour.
"So people can still travel along the A5 and not have to use the A55 route."
Clwyd South AM Karen Sinclair said she could understand the anxiety of local businesses, particularly as the tourist season started.
"Small shops and businesses depend so heavily on the traffic on that road and the tourism that comes through," she said.
Ms Sinclair has asked Enterprise and Transport Minister Andrew Davies to consider using the old A5, which runs parallel to the new road, as the diversion to "minimise loss of traffic".
She added: "Back in February there were problems with the rock anchors and a lot of exploration went on, but recently they've found the problem is much much bigger.
"There is no doubt that there is a real problem with this road and the bottom line has to be safety.
"To try and minimise any impact on traders is absolutely imperative and I'll be working very hard with Andrew Davies and with his officers to make sure this happens."