The event was an unprecedented diplomatic effort by Sinn Fein, the former political wing of the IRA and a party that has always refused to take its seats in Westminster.
The bill would also stop future investigations and civil actions related to the Troubles, although it does not completely close the door to criminal proceedings.
At a rare meeting with a multi-party group of MPs in Westminster on Tuesday night, Ms McDonald called on backbenchers and Conservative parents to speak out against the prime minister’s plan to break protocol.
“We now have a total attack, a total attack on the Good Friday Agreement,” he told the meeting, which was attended by a majority of left-wing Labor MPs, the SNP and Plaid Cymru, as well as veteran Conservative Brexiteer Sir Bill Cash.
“And most alarmingly, we have an administration, a prime minister at 10 Downing Street who is playing fast and loose, a very dangerous game of brinkmanship, with everything that has been achieved over the last quarter of a century. .
“This is a very serious and very serious situation that should catch the attention of all members of the House of Commons and all peers in the House of Lords.”
During a speech that provoked frequent applause from an audience that included former Labor leader Jeremy Corbyn and his former leaders John McDonnell, Richard Burgon and Rebecca Long-Bailey, he insisted that Sinn Fein wants good relations with the number 10.
He said: “This should be challenged and we should not just discuss it from the opposition banks. This should be challenged from the government itself because it is very, very wrong.
“We don’t want to look down on Boris Johnson or any of his colleagues, but we have no choice but to challenge him in the strongest terms.”
The meeting in Westminster was held after the families of the victims of Troubles told the Prime Minister that the controversial legislation of the legacy of the UK government is “an affront to all modern standards of decency”.
Protests also took place in Belfast and Londonderry as MPs debated the inherited plan in the House of Commons, which would offer immunity to people believed to have co-operated with an information retrieval agency.
Michelle O’Neill, Sinn Fein’s vice president, said most people in Northern Ireland support the Protocol, which created the Irish Sea border and introduced customs controls on British goods.
“The British government must stop complying with the DUP,” Ms O’Neill told the BBC, leading Sinn Fein to a historic first majority in the May 5 elections to the Irish Assembly. of the North.
“The voice of the DUP does not reflect the broader vision at home,” he said, noting the pro-protocol majority in Stormont after the election that will make him prime minister if shared power is restored.
The DUP, which lost its majority, says the Protocol, which prevents a hard border on the island of Ireland, is raising the cost of living and creating a gap between Northern Ireland and the rest of the UK.
He has refused to share power in Stormont and has blocked the appointment of a new Speaker in the Assembly until the Protocol is withdrawn or replaced in negotiations between the United Kingdom and the EU.