Labour has called on the government to take action to tackle the continuing trade disruption between Great Britain and Northern Ireland.
Some companies are struggling to deal with the requirements of the new Irish Sea border.
That is leading to temporary shortages of some products in a growing number of NI supermarkets.
The government says the flow of goods between Great Britain and Northern Ireland has been smooth overall.
In a letter to their counterparts, Shadow Secretary of State for Northern Ireland Louise Haigh and Shadow Chancellor of the Duchy of Lancaster Rachel Reeves urged the government to act as freight volumes start to increase over the next week.
They say there needs to be better government guidance for GB companies which are shipping to NI.
They have also questioned whether the new Trader Support Service is adequately resourced.
The shadow ministers said: "The failure to properly prepare GB businesses for the huge changes in the trading relationship with Northern Ireland is having real consequences.
"Incredibly rather than taking concrete steps to minimise disruption, the secretary of state for Northern Ireland is in denial and simply pretending the border does not exist.
"The Northern Ireland Protocol has to be made to work - that's why we need urgent action to iron out these issues."
A government spokesperson said: "There are no significant queues at NI ports and supermarkets are reporting healthy supplies into their Northern Ireland stores.
"We recognise the need to provide as much support to the haulage sector as possible as industry adapts to new processes.
"We have been engaging intensively with the Irish authorities and hauliers on the issues that have been encountered for goods transiting through Dublin Port."