Conservative vice chair Ben Bradley has resigned from his position over the government's Brexit plan - warning it would risk "handing Jeremy Corbyn the keys to Number 10".
The Mansfield MP is the latest figure to quit in protest over the agreement reached by Theresa May's Cabinet at Chequers last week.
Boris Johnson and David Davis left their roles as Foreign Secretary and Brexit Secretary respectively.
In his resignation letter, Mr Bradley said he took the decision with "great regret".
I have come to the conclusion that I cannot in good faith be a good spokesperson for the party or for the Government on this issue, and I cannot with any sincerity defend this course to my electorate, 71% of whom voted to leave.
Mr Bradley also said the Chequers plan would damage the UK's opportunities to develop global trade and be "an outward-looking nation in control of our own destiny" following Brexit.
Being tied to EU regulations and the EU tying our hands when seeking to make new trade agreements will be the worst of all worlds," wrote the Mansfield MP.
Fellow vice chair Maria Caulfield also quit her role, citing concerns over the government's Brexit position.