Labour lawmaker Chuka Umunna had proposed an amendment to the Conservative government's policy programme on Thursday calling for Britain to remain in the single market and customs union.
The motion was defeated by 101 votes to 322, with most Labour lawmakers following the party line and abstaining.
But 49 lawmakers supported the amendment, defying Corbyn's orders to stick to the party's policy that Britain should leave the single market.
Struggling British PM faces confidence vote
Among those who voted in favour of the amendment were shadow housing ministers Andy Slaughter and Ruth Cadbury and shadow Foreign Office minister Catherine West, all of whom Corbyn later fired.
Another lawmaker Daniel Zeichner also resigned as shadow transport minister before the vote as he planned to oppose the official party line.
"I'm a passionate pro-European and straight-forward politician so I've taken hard decision to resign as shadow minister to back Single Market," Zeichner wrote on Twitter.
I'm a passionate pro-European & straight-forward politician so I've taken hard decision to resign as shadow minister to back Single Market.
— Daniel Zeichner (@DanielZeichner) June 29, 2017
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