Liberal Democrat leader Nick Clegg is facing mounting pressure over tuition fees after one of his MPs made clear he was ready to quit the Government.
Ministerial aide Mike Crockart said his “morals” meant he was “100%” certain to vote against controversial reforms when they come before the Commons this week.
The comments emerged after Transport Minister Norman Baker hinted that he could also choose to go rather than renege on the Lib Dems’ pre-election pledge to oppose any fee hikes.
Deputy Prime Minister Mr Clegg is due to make a last-ditch effort to head off a crisis when he addresses his parliamentary party on Tuesday night.
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 the principle of collective responsibility for ministers still applied.
However, there were signs that opposition within the party was hardening despite efforts to strike a deal.
Speaking to the Evening Standard, Mr Crockart said: “I have got better standards and morals than that. If we have got nothing else in this world, we have got principles.
“I will be voting against 100%. I’m not going to be pushed out. Resigning probably will be the only option.”
Asked on BBC One 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.”
He added: “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.”