Labour has faced an onslaught from all sides after most of its MPs backed Theresa May's plans to trigger the process for quitting the European Union by the end of March on condition the PM reveals her strategy.
The Opposition was accused of handing the Conservatives a "blank cheque" for Brexit after 149 of its MPs, including leader Jeremy Corbyn, trooped through the voting lobbies with the Government.
Labour MPs who did not back the move were "named and shamed" on social media by the Tory party for failing to "respect" the June 23 referendum result.
The Prime Minister took the wind out of the sails of a potential Tory rebellion in the symbolic Commons vote after conceding on Tuesday to set out the direction Brexit negotiations will take.
An amendment to a Labour motion calling for that to happen was put down by the Government, explicitly challenging members of all parties to support the timetable for activating Article 50.
A technical vote formally adding the two elements together was overwhelmingly passed with a majority of 372, despite 23 Labour MPs joining other opponents in trying to derail it.
MPs then backed the amended motion calling on the Government to publish its Brexit plan and to trigger Article 50 before March 31, by 448 votes to 75.
Europhile Tory Ken Clarke was the lone figure in his party to oppose the move.
The former chancellor said Mrs May's promise to reveal her plan was "extremely vague", and called for it to be set out in detail in a White Paper for publication before the invocation of Article 50.
Shadow ministers Tulip Siddiq, Catherine West and Daniel Zeichner along with fellow Labour MPs Rushanara Ali, Ben Bradshaw, Jim Dowd, Paul Farrelly, Mike Gapes and David Lammy voted against the motion.
Tory former cabinet minister Iain Duncan Smith told Sky News the vote was a "historic moment".
"They have had their bluff called, I suppose. They have had to vote to give us a date, so that is a real blank cheque for the Government.
"That means that no matter what happens now in Parliament, Labour is signed up to the principle that by March 31 next year the Government will have been able to invoke Article 50.
Lib Dem leader Tim Farron accused Labour and the Conservatives of a stitch-up.
"Labour and the Tories are holding hands towards a hard Brexit," he said. "There should be democracy throughout this process, not a parliamentary stitch-up that denies the public a say over the final deal.
"It's clear that only the Liberal Democrats are providing a real opposition to the Conservative Brexit Government and striving to keep Britain open, tolerant and united."
Shadow Brexit secretary Sir Keir Starmer insisted Labour's hands had not been tied, telling Sky News: "If the plan the Government comes up with is a late, vague plan, they can expect further challenge.
"If they haven't produced a plan by the time we get the legislation, then it will be open to us to put down amendments saying what the prerequisites of the plan are."
The Conservative Party press office used its Twitter account to "name and shame" Labour MPs who failed to back the motion.
After each opponent's handle, it added the phrase "won't respect referendum result - Labour are out of touch with ordinary working people #BrexitDebate".
Some 51 SNP MPs, Green Party MP Caroline Lucas and five Liberal Democrats were among others to vote against the proposal.