The leaders of Italy’s right-wing parties have pledged to deport hundreds of thousands of migrants if they win the March 4 parliamentary election, a promise that may win votes but will be hard to keep.

A center-right coalition that includes former Prime Minister Silvio Berlusconi’s Forza Italia (Go Italy!) and the anti-immigrant League is leading in opinion polls, in part because of their hardline on immigration.

Surveys show Italians are increasingly uneasy after more than 600,000 migrants reached Italian shores by boat in four years. At the weekend, a neo-Nazi wounded six migrants in a shooting spree in central Italy, thrusting immigration to the heart of the election campaign.

“These 600,000 people, we will pick them up using police, law enforcement and the military… everyone can help identify them by pointing them out, and they will be picked up,” said Berlusconi on Monday.

“Then we’ll use state ships and airplanes to take them back to their countries of origin,” he said.

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League leader Matteo Salvini said irregular migrants would be rounded up and sent home “in 15 minutes” if he and his allies take power.

But the reality is that deportations are expensive, time consuming and complex. It would take years to repatriate those irregular migrants already living in Italy and thousands continue to arrive each month, mostly by boat from North Africa.

“For many years people have been saying more irregular migrants should be sent home, but in fact it has not been possible,” said Flavio Di Giacomo, a spokesman for the United Nations’ International Organization for Migration in Rome.

Interior Minister Marco Minniti said he wanted to increase expulsions, but deported 6,500 people last year against 5,200 a year earlier. “If we wanted to repatriate 600,000 irregular migrants, and we could send 200 per working day, it would take more than 15 years,” said Senator Luigi Manconi, a member of the ruling Democratic Party (PD) who next month will take charge of the country’s anti-racism office.

The cost of deportations is high. Forced returns require that migrants be put in detention centers before departure, planes must be chartered and wages paid – two guards for each migrant. In 2016, the repatriation of 29 Tunisians from Italy cost 115,000 euros ($141,795). On average, repatriations conducted jointly with EU border agency Frontex cost 6,500 euros each, an EU observer study found last year.