Labour MP Vicky Foxcroft has resigned from her post as a government whip over Sir Keir Starmer's plan to cut benefits.
She wrote in a letter to the prime minister that she could not vote "for reforms which include cuts to disabled people's finances".
The former shadow minister for disabled people becomes the first MP to quit the government over the controversial welfare reform plans.
The MP for Lewisham North wrote that the benefits system is in "desperate need of reform", adding: "I absolutely understand the need to address the ever-increasing welfare bill in these difficult economic times, but I have always believed this could and should be done by supporting more disabled people into work.
"I do not believe that cuts to personal independence payment (PIP) and the health element of Universal Credit should be part of the solution."
Foxcroft said she has "wrestled" with the decision over whether to resign, but said: "Sadly it is now seems that we are not going to get the changes I desperately wanted to see.
"I therefore tender my resignation as I know I will not be able to do the job that is required of me and whip 鈥� or indeed vote 鈥� for reforms which include cuts to disabled people's finances."
To read the government's response, tap here.