There were angry scenes on Monday night as the bill enabling the government to trigger Article 50 cleared the Lords.
Lib Dem Lord Oates accused Labour of being prepared to "concede everything", and the opposition's leader in the Lords, Baroness Smith, responded that his party was giving people "false hope".
The two parties had teamed up to help inflict defeats on the government concerning the rights of EU citizens and parliamentary approval for a Brexit deal.
But that co-operation went out the window when MPs rejected those amendments - with Lib Dems determined to insist on them and Labour prepared to defer to the Commons.
What did the parties say about each other?
A Labour source in the Lords told the BBC it was "fairly obvious grandstanding" by the Lib Dems, and geared towards content for their campaign leaflets.
"It's pretty unforgiveable to build up false hope with people genuinely worried about their future in Britain, when you already know that MPs were ready to dig in behind the government," the source said.
For their part, the Lib Dems' Europe spokesperson Baroness Ludford accused Labour of "waving through the government's plans" and "lining up with the Conservatives as they drive forward with a hard Brexit".
Where do they go from here?
It's not just on Brexit that the two biggest opposition parties have a track record of forming alliances - they have trooped through the lobbies together to impose government defeats on bills dealing with issues from higher education to housing.
Baroness Ludford seemed sanguine about their chances of coming together again, saying: "The Liberal Democrats will continue to work with peers from across the House to fight for the issues we agree on."
But the Labour source predicted "residual tensions", adding: "I can't imagine there'll be much demand here to organise a 'progressive consensus summer drinks' gathering.
"Our respective leaderships will of course continue to keep things business-like."