Councillors in Patrick Mercer's constituency of Newark, where he has a 16,000 majority, have expressed their shock at the news of his resignation.
Councillor Peter Duncan said he always thought of Mr Mercer as "a very solid citizen".
He added: "If this news is true then I am shocked. I thought he was a very strong individual with a strong point of view. He will be missed."
Another Tory councillor Derek Evans said: "I'm very surprised at the news. I've a lot of trust and faith in Patrick. I have utter faith in him as an MP."
Conservative MP Patrick Mercer has been accused of breaking parliamentary rules by offering to provide a Commons pass for lobbyists.
The Conservative MP, who is alleged to have lobbied on behalf of Fiji, posed several questions about the country to Parliament this year.
Patrick Mercer MP spent 25 years in the Army before entering politics.