Liberal Democrat leader Nick Clegg is preparing a last-ditch appeal for his MPs to avoid a damaging three-way split over tuition fee hikes.
Frantic negotiations have been continuing as some members of the Government, including transport minister Norman Baker, appeared willing to quit rather than back the controversial proposals.
Mr Clegg will hold a crunch meeting with his parliamentary party on Tuesday night at which he is expected to urge them to present a united front.
Lib Dem grandee Lord Ashdown has also appealed for MPs not to breach the coalition agreement by voting against the plans on Thursday, while Downing Street warned that ministers are still subject to the principle of collective responsibility.
However, there were signs that opposition within the party was hardening despite efforts to strike a deal.
Asked on BBC1 South East’s Politics Show whether he would be backing the change or abstaining, Mr Baker said: “Or voting against. There are three options and, to be honest with you, I genuinely haven’t decided.
“It’s an option if you resign. There are three options on the table and I haven’t yet decided what I’m going to do.”
In a bizarre episode, someone claiming to be Mike Crockart, the parliamentary private secretary to Scottish Secretary Michael Moore, told the Evening Standard and the BBC he was also on the verge of resigning.
Questions were only raised about the impersonator’s identity when colleagues realised the voice on air was not that of the Edinburgh West MP.
Mr Clegg and Business Secretary Vince Cable have publicly stated that they would like to vote for the package, which trebles the maximum annual charge to £9,000, although the idea of a mass abstention as allowed under the coalition deal has been floated.