Eurosceptic firebrand Nigel Farage will suggest the forthcoming EU referendum could become a vote on whether the UK wants to be in a political union with Turkey when he addresses the European Parliament on 9 March.
The Ukip leader will also claim that Recep Tayyip Erdogan's government "bullied and blackmailed" the EU into accepting its proposals to help address the ongoing migrant crisis.
Farage's remarks come after Brussels agreed to speed up a €3bn (£2.3bn) payment to Turkey and set forward plans to allow Turkish nationals to travel to the EU visa-free by June 2016.
"It's outrageous that the EU has allowed itself to be bullied and blackmailed by Turkey in this way," Farage will declare. "That the British taxpayer will have to shell out another £500m is unacceptable."
"Most worrying of all, it is now clear that Turkey will be fast-tracked into membership of the EU – a position agreed by David Cameron and William Hague.
"Perhaps this referendum on 23 June will become a referendum on whether we wish to be in a political union with Turkey. A vote for Remain is a vote for Turkey."
UN and Amnesty raise concerns
The United Nations (UN) has also raised concerns about the EU/Turkey deal, particularly regarding a proposal to send Syrian refugees back from Greece to Turkey. Under the plan, for each Syrian deported another in Turkey gets settled in the EU.
"We hope that individuals returned to Turkey who have specific resettlement needs, such as family reunification, would be considered for the resettlement/admission programme to the EU," said the Office of the UN High Commissioner for Refugees (UNHCR).
Turkey already houses around 2.75 million refugees, many of which are from neighbouring Syria, and more than 130,000 migrants have crossed the Mediterranean this year so far, according to the International Organisation for Migration.
Amnesty International branded the deal a "death blow" to the right to seek asylum. "The idea of bartering refugees for refugees is not only dangerously dehumanising, but also offers no sustainable long-term solution to the ongoing humanitarian crisis," said Iverna McGowan, head of Amnesty International's European institutions office.
David Cameron promised in 2015 that the UK would take 20,000 Syrian refugees by the end of the parliament, which comes to an end in 2020. But the prime minister stressed the government would only take refugees from camps bordering Syria in a bid not to draw people across the Mediterranean.