Around 40 members are understood to be preparing to vote for a planned amendment to the Education and Skills Bill, to ban academic selection from England's remaining 164 grammar schools.
The plan comes from a group of Labour MPs who are generally unhappy about the Government's school policies, and who may also try to amend the Bill to target faith schools and academies.
If they fail, they may vote against the Bill in its entirety, jeopardising the beleaguered Prime Minister's key goal of making education or training compulsory for young people up to the age of 18.
The Conservatives have yet to decide how they will vote on the legislation, but if they joined the backbenchers, the Government's majority could be in peril.
Ian Gibson, Labour MP for Norwich North, told The TES: "There are 40 people who have got the bottle to have a go, and in the current climate a lot of things are going to be up for grabs.
Dr Gibson was one of 46 Labour MPs who voted against Tony Blair's controversial trust school plans in 2006. They were passed with Conservative support, and Dr Gibson said a "large cadre" of Labour MPs had remained unhappy about their party's education policy ever since.
"It is all about the disgruntlement that nothing is going to change because the Prime Minister has changed," said Dr Gibson.
"Real Labour people are disappointed that we are going through with the same kind of policies."
He said the decisions by Ed Balls, the Children, Schools and Families Secretary, to attack admission code breaches by faith schools, and limit academy curriculum freedoms, were a step in the right direction.
"Ed Balls is a hope," said Dr Gibson. "He has got the right kind of feelings about education but whether he can carry it off in Cabinet is the question."
The last attempt to abolish the 11-plus exam was an amendment to the Education and Inspections Bill, which was defeated by 415 votes to 115 in 2006.
The Sunday Telegraph reported this week that some grammar schools were receiving more than pound;1,700 less per pupil than their neighbours because of a Government directive ordering councils to spend more on schools with disadvantaged pupils.