The MP for Batley and Spen has described the loss of colleagues to new 'breakaway party' The Independent Group as "heartbreaking".
Seven Labour MPs, namely Luciana Berger, Ann Coffey, Mike Gapes, Chris Leslie, Gavin Shuker, Angela Smith and Chuka Umunna, founded the breakaway on Monday and were joined by Joan Ryan yesterday.
Today, Tory MPs Anna Soubry, Heidi Allen and Sarah Wollaston brought the group's membership to 11.
After hearing the news on Monday, Labour MP Ms Brabin tweeted: "Heartbreaking to lose colleagues in this way. Only by working together as a broad church can we change the lives for our constituents. @UKLabour and @CoopParty have long-standing traditions to support those most in need and with ambition to fulfil their potential. A sad day."
In reply to a constituent airing his views on the need for the Labour party to change its direction, Ms Brabin replied:
"There are other MPs who share similar concerns to the ones who have now left but are staying and working hard to ensure these rotten Tories are given the push so politics works for those who are doing the slog in this country rather than those with vested interests."
A spokesperson for Ms Brabin said she has nothing more to add on the matter.