Kerry McCarthy has resigned as shadow Defra secretary in protest of Jeremy Corbyn's leadership of the Labour Party.
The move comes as members of the shadow cabinet have either been sacked or resigned in the wake of the Brexit vote.
"The referendum result was a huge disappointment," McCarthy said in a letter to the Labour leader.
"We now face the challenge of negotiating our future relationship with the rest of Europe.
"Vital protections won through our EU membership must not be jettisoned.
"I believe a new leader is needed to take on the challenges: steering out way through the very difficult period facing the country."
Fresh appointments come after a turbulent Sunday, which began with Mr Corbyn sacking shadow foreign secretary Hilary Benn.
Fourteen members, including Lilian Greenwood, Lucy Powell, Ian Murray, Gloria De Piero, Chris Bryant and Heidi Alexander also tended their resignations from the shadow cabinet after Benn's sacking, and more are expected to follow.
Former shadow education secretary Lucy Powell, who resigned on Sunday, insisted it was not a "planned coup" against Mr Corbyn but instead a reaction to the "seismic" events which have shaken Westminster in recent days - the European Union referendum result and David Cameron's resignation.
Labour Party leader Jeremy Corbyn has started a reshuffle of his shadow cabinet, following a revolt asgainst him.
