The EU rejects this claim. An EU Commission spokesperson told CNN that the EU was sticking to its side of the deal, pointing out that the EU had committed over $6.6 billion dollars to handling the crisis, $3.5 of which has already been spent. The source pointed out that Turkey's objections might have more to do with the fact that the money does not go directly to the Turkish government.

Whatever the truth, the threat this poses to the EU is significant. Migration has been a hot-button issue in Europe for some time. And the EU's lackluster approach to handling the crisis has left it in a position where a leader like Erdogan can effectively hold a gun to Brussels' head and start making demands.

The 2016 agreement came about after Syria's multi-year civil war saw unprecedented numbers of people fleeing violence trying to enter the EU through Greece's land and sea borders with Turkey.

Migration had become politically toxic among EU member states. Some leaders, most notably Germany's Angela Merkel, were eager to ease the humanitarian crisis, after reports emerged of refugees being subjected to horrendous living conditions and shocking images were published of bodies washing up on European shores after boats -- overloaded with refugees -- sank.

However, welcoming the influx of migrants from Syria aided the growth of Europe's far-right populists. Parties across the bloc used it to bash the EU's refugee policies and argue for tighter border control.

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A migration crisis and disagreement with Turkey is the last thing Europe needs right now - CNN