The committee has taken the unusual step of asking Mr Buckland to explain how he believes the controversial bill complies with global law.
"We know how seriously you take your oath of office and responsibility to uphold the rule of law and when you appeared before the committee in July you spoke passionately on the subject", the committee said.
Why is Britain changing the law? The two sides are trying to strike a new trade deal by then, but talks have bogged down.
Writing in Saturday's Daily Telegraph newspaper, Johnson said the EU's stance justified his government's introduction of new legislation to rewrite its Brexit withdrawal treaty - a bill that is causing deep alarm among his own MPs.
The British in Europe coalition, in a joint statement with the3million group representing European Union citizens in the United Kingdom, says many people are now anxious about implications for their rights and futures if the citizens' rights part of the WA was also put at risk.
But Britain is pressing one of the EU's most sensitive buttons - fear that a post-Brexit Britain could become a much more deregulated free-market competitor with access to European Union markets by using selective state aid.
"It's not about if we implement the (EU) Withdrawal Agreement and the Northern Irish Protocol, it's how we implement it", business minister Nadim Zahawi said.
The British government says trade barriers between Northern Ireland and the rest of the United Kingdom could undermine Northern Ireland's place within the United Kingdom and destabilise the peace settlement that ended decades of violence.
Irish premier Micheal Martin, who spoke by phone with UK Prime Minister Boris Johnson on Wednesday evening, said such an outcome would be "gross irresponsibility" on top of the economic havoc inflicted by COVID-19.
A legal opinion circulated to MPs by the Attorney General Suella Braverman on Thursday argued that Parliament was sovereign in domestic law and was entitled to pass legislation which breached the UK's treaty obligations.
In the Commons, senior Tories have begun tabling an amendment to the bill which they said would limit the powers it gave to ministers in relation to the WA.
"The withdrawal agreement is not open for renegotiation and that we expect that the letter and the spirit of the withdrawal agreement will be fully respected", European Commission Vice President Maros Sefcovic said.
The Internal Market Bill, which will be formally debated in the House of Commons for the first time on Monday, addresses the Northern Ireland Protocol - the part of the Brexit Withdrawal Agreement created to prevent a hard border returning to the island of Ireland.
First of all, it should be noted that the government does not say that it is trying to denounce the entire withdrawal agreement.
But he signalled he would be ready to be thrown out the Conservative parliamentary party if necessary.
"We are not going to carry out any "empty chair" diplomacy, that is quite clear", he added.
Talks between London and Brussels on a future trading relationship are deadlocked as both sides struggle to prise apart almost 50 years of economic integration, after British voters opted for a divorce.
The row erupted as the latest round of trade talks - also taking place in London - ended on Thursday with both sides acknowledging that "significant differences" remain. Johnson has said Britain will walk away if there is no agreement by October 15.
Earlier this week, the Speaker of the US House of Representatives Nancy Pelosi said there will be "absolutely no chance" of a US/UK trade deal if Boris Johnson overrides the Brexit deal with Brussels.
Without a deal, British freight firms have warned there could be logjams at ports and supplies of key goods in Britain could be severely disrupted starting January 1.