Foreign Secretary Margaret Beckett has suffered defections from her local Labour Party over her handling of the Middle East crisis.
"The people of Lebanon and Israel are suffering," said Mrs Beckett
The Liberal Democrats say 37 Labour members in Mrs Beckett's Derby South constituency have defected to them.
The defectors, who include some local Labour Party officials, are angry that the government refused to call for an immediate ceasefire in Lebanon.
Labour says Mrs Beckett has been working for a sustainable ceasefire.
Mohammed Rawail Peeno, who was chairman of the Arboretum branch of Derby's Labour Party, said he and the other defectors were protesting against the mishandling of the Lebanon crisis.
"When Margaret Beckett refused to back a ceasefire and instead sided with George Bush it was the breaking point for us," he said.
"New Labour have abandoned the beliefs that led me and thousands of others to join Labour in the first place."
Lib Dem leader Sir Menzies Campbell said: "These defections in the foreign secretary's own seat are significant.
"The government's position on the Middle East and Iraq shows just how out of touch it is with many in its party and the majority of the general public."
A Labour Party spokesman said "on going local factors arising from a selection process last year" for a local council seat had led to the defections.
"It is always disappointing when any members decide to leave the Labour Party," he said.
"It is important that the foreign secretary and the prime minister continue to work hard to achieve a sustainable ceasefire in Lebanon, something we are sure all Labour Party members would unite around."
A local Labour source said the defections were about selections and "over inflated egos", not the Middle East.