The whips, who try to organise their MPs voting, are concerned that the Chancellor’s budget may not get through parliament.
If rejected it would be the first budget to be thrown out since William Gladstone’s budget in 1885.
Whips have been making extra demands to MPs by making clear the huge opposition there is to relaxing any planning rules in the green belt.
Theresa May is resisting calls from Philip Hammond to free green belt land for housing as he seeks radical cost-free measures for the budget.
Mr Hammond is facing a tough budget given the minority government, Mrs May’s refusal to build on green belt and the lack of economic flexibility.
The Treasury has said it wants to encourage housing developments and they are a part of tomorrow’s budget.
However, Mr Hammond does not want to borrow significant amounts to invest in housebuilding so options are limited.
One MP told the Times: “The whip said they themselves knew it was madness, but made clear that it would be useful if they were able to add my name to the list of people opposed to this, to feed back to the Treasury.”
Another Tory MP said the whips had targeted members representing seats in the south of England.
They said: “This isn’t normal.
“It’s a function of perceived weakness in No 11, as was shown on The Andrew Marr Show.
“Hammond says things that set hares running, he lacks political antennae.
“This may be an attempt to inject some political thinking into the operation.”
Mr Hammond has been arguing with the Cabinet for months for some of the green belt to be reclassified so it can be built on.
The parliamentary private secretary to Mr Hammond, Kwasi Kwarteng, reportedly urged the fellow private secretaries to get behind Mr Hammond’s budget.