The British government has denied misleading Northern Ireland politicians over customs checks post-Brexit.
Northern Ireland spokesman James Younger said there would be "unfettered access" for Northern Ireland businesses to the UK market.
But he acknowledged there would be requirements for "live animal checks and agrifoods, building on what already happens at Larne and Belfast".
Former Ulster Unionist leader Reg Empey had asked the government whether customs posts would be established in Northern Ireland from next year and how this was compatible with assurances on free access.
Mr Younger said the protocol was a "practical solution to prevent a hard border on the island of Ireland" and made clear that Northern Ireland "remains an integral part of the UK and its internal market".
This included legislating to guarantee "unfettered access for Northern Ireland businesses to the UK market".
In a virtual Lords urgent question, Mr Empey said ministers had repeatedly assured parliament that no checks would take place on goods moving to or from Northern Ireland after transition.
"There is a widespread feeling that members have been consistently misled," he added.
Mr Younger said: "We've always been clear that there will be requirements for live animal checks and agrifoods, building on what already happens at Larne and Belfast."
He said ministers wanted to work with Northern Ireland businesses and the Executive to ensure that "new administrative procedures are streamlined and efficient".
The government wanted to ensure "optimum flow of trade", Mr Younger insisted.
Labour former Northern Ireland secretary John Reid of Cardowan warned that a "clear breach of a vow given by ministers" undermined trust in the government.
But Mr Younger said he was not sure what the breach was, adding: "We have always said there will need to be light-touch checks particularly for live animal checks and agrifoods coming from the internal markets in the UK across to Northern Ireland."
Liberal Democrat Joan Bakewell of Hardington Mandeville said the British Prime Minister had repeatedly said he could not see any circumstances in which there would be a need for checks on goods going from Northern Ireland to Britain.
Ms Bakewell called for an extension of the transition period, warning that no deal with the EU would have implications for the Northern Ireland protocol.
But Mr Younger ruled this out, saying the government had no intention of extending the transition period.
Angela Smith, Labour's leader in the Lords, said she was "absolutely flabbergasted" by Mr Younger's responses.
Ms Smith said PM Boris Johnson had said that if there were any customs forms issued, they should be "thrown in the bin".
Mr Younger said Mr Johnson was adamant that there would be "unfettered access".