Tory backbenchers today set out a "shopping list" of powers they want David Cameron to reclaim from the European Union.
A report called for the clawing back of key Brussels controls over justice, labour rules, energy, agriculture and defence.
It also upped the pressure on the Prime Minister by insisting the renegotiated relationship must be put to a referendum.
The Fresh Start project document - put together by MPs Andrea Leadsom, Chris Heaton-Harris and George Eustice - emerged with coalition tensions running high over the issue.
The Liberal Democrats have pledged to block any attempt at loosening ties.
But Foreign Secretary William Hague is due to appear at the launch of the report this evening - in what will be taken as tacit support for the MPs' approach.
The document said changes being put in place to cope with the crisis in the eurozone present a major opportunity for the UK to get a better deal.
It suggested Britain could insist on a veto for EU financial services regulation in recognition of the City's importance to our economy.
The document floated the prospect of withholding billions of pounds in contributions to European development funds if they are not reformed.
The authors admitted that would be a "breach of the UK's EU treaty obligations" and the Government could end up in the courts.
But they added: "This action might help force a meaningful negotiation if other member states had previously refused to take the UK seriously."
The report highlighted the need for radical reform of the Common Agricultural Policy (CAP), saying Britain is currently making a net contribution of £1 billion per year.
It warned that the fallout from a unilateral withdrawal from CAP mean that would "not provide a sustainable long-term solution".
However, the threat could be used as a "negotiating tactic".
On fisheries policy, the MPs urged changes to protect Britain's small-scale fishing fleet and ensure stocks are sustainable.
They also backed action to restrict rises in the EU budget and reforms to make its institutions more accountable.
If other members will not agree to reduce regulation of social and employment law, the UK could "take back control" by demanding opt-outs from "intolerable" proposals.
The report raised concerns about immigration from EU states, proposing options that would give the government more control.
One is to seek an EU treaty change that would allow skills and earnings thresholds to be imposed.
But the MPs added that simply ignoring free movement rules and limiting numbers, or refusing to pay benefits, could be effective.
"Such action would provoke a major row with other EU countries, which would be likely to impose similar restrictions on British migrants," the document said.
"However, it could bring other member states back to the negotiating table over EU rules."
Britain should also use its leverage to insist that the EU's common security and defence policy (CSDP) focuses on complementing Nato's activities, rather than competing or duplicating.
The Government could either start vetoing CSDP initiatives where possible or opt out from the arrangements altogether, according to the document.
The report said: "Once the plan for reform is complete, then begins a significant renegotiation and this must be followed by a referendum.
"The British people must be given their say on whether to remain in the EU with a reformed relationship that gives powers back to the UK, or whether to withdraw from the EU to make our own way in the world."
Ms Leadsom said: "Events in Europe mean that the way the EU operates is bound to change significantly.
"Over the coming years, there will be a series of opportunities for the UK to take back power from Brussels. This is the perfect chance for us to negotiate a radically different relationship with the EU, one which properly serves Britain's interests.
"We believe strongly that the Government must adopt an approach to these negotiations which is completely different from previous practice.
"There must be no more of Britain's traditional reserve - we must get the best deal for Britain and not worry about others' feelings.
"This is not the time for Whitehall's 'two key points' negotiating approach - we need a shopping list of requirements, which will enable ministers to secure the right package."
Mr Heaton-Harris added: "When the renegotiation is complete, the British people must have their say - there must be a referendum on what any new relationship looks like."
Mr Eustice said: "Those who say it is not possible to renegotiate Britain's relationship with the EU are wrong.
"Whatever happens to the euro, change is on the cards. Some of our proposals can be advanced alongside the current budget negotiations, others will be matters for the next Conservative manifesto which is the next step."