Greek islands could find themselves flooded with refugees and migrants with the summer tourism season set to start if a European Union swap deal with Turkey falls apart after six countries balked at sending three billion euros ($3.68 billion) in the next installment.

Turkish President Recep Tayyip Erdogan, already pushing provocations in the Aegean and disdaining EU calls to rein himself in, had already threatened to let human traffickers unleash more refugees and migrants with the Greek islands near his country’s coast already overwhelmed with more than 15,000 of them, and another 50,000 on the mainland.

The March 2016 deal, along with Europe closing its borders and dumping the problem on crisis during its long-running economic crisis, had nearly shut off the flow after more than a million had come to the EU.

But the numbers have begun picking up again with more arriving on the islands and with Greece and Turkey at near-firing loggerheads over Turkish fighter jet invasions of Greek airspace and warships cruising past Greek islands and the two country’s leaders firing off fusillades of criticism at each other.

The deal would bring Turkey six billion euros ($7.32 billion), visa-free travel for its citizens in the EU and faster track entry in the bloc after more than a decade of trying, but was suspended effectively and has seen only a relative handful returned.

According to Germany’s Der Spiegel, officials from Germany, France, Austria, Sweden, Denmark and Finland want the European Commission to pay for the delayed second installment of three billion euros, an idea rejected by President Jean-Claude Juncker.

A German official warned that money would only be disbursed if Turkey presses on with the agreed-to infrastructure works but Erdogan has been at a war of words with EU officials even as he pushed them at a critical meeting in March to speed the deal.

Prime Minister and Radical Left SYRIZA leader Alexis Tsipras, who called Erdogan a “Sultan,” said it’s time to pull back the rhetoric, said Kathimerini, urging Turkey to release two Greek soldiers facing trial after accidentally crossing the border while on patrol in bad weather.