Frontbench Labour rebels who defied Jeremy Corbyn over the Brexit Bill will not get the sack, but a written warning.
The reprimand emerged after Labour's chief whip Nick Brown met with Mr Corbyn to decide what disciplinary action would follow after 52 MPs ignored the leader's orders and voted against triggering Article 50.
The light touch reaction was put down to the "extraordinary circumstances" of the referendum aftermath, according to Labour sources.
Rebels will receive a written warning, and will be expected not to defy a three-line whip again.
Labour sources told the Press Association that Mr Corbyn believes it will "not be viable" for someone to remain in the Shadow Cabinet if they ignore another three-line whip.
Mr Corbyn is clear that this is the "final warning" to Brexit rebels on the issue, the source said.
The Labour leader was forced to reshuffle his top team after a number of members quit ahead of voting against triggering Article 50.
However, 11 shadow ministers, and three whips, remained in their posts despite defying the leader's command.
A large swathe of the parliamentary party ignored Mr Corbyn's orders and tried to stop the Brexit Bill passing on Wednesday.
The 11 frontbenchers who voted against the Bill in its final Commons stage without quitting their jobs were Rosena Allin-Khan, Kevin Brennan, Lyn Brown, Ruth Cadbury, Rupa Huq, Chi Onwurah, Stephen Pound, Andy Slaughter, Catherine West, Alan Whitehead and Daniel Zeichner.
The whips were Thangam Debbonaire, Vicky Foxcroft and Jeff Smith.