Poland expects a mass exodus of 100,000 to 200,000 of its citizens from the U.K. following Brexit.

According to the Polish Development Ministry, 10-20% of Polish nationals could return to their country of birth. According to the U.K.’s national statistical service (ONS), in 2015 Poland became the single most common non-UK country of birth in the U.K., with an estimated 831,000 residents. That corresponds to 9.7% of the total non-UK born population of the UK, which amounted to approximately 8,6 million at the time.

Polish authorities estimate that up to one million Poles could be living today in the U.K., most of whom emigrated since 2004 when Poland joined the EU.

“The situation around Brexit combined with improvement in the socio-economic situation in Poland may mean that some Poles (an estimate of 100,000-200,000) presently living in Great Britain will decide to return,” Poland’s Development Ministry told a member of Parliament according to Reuters.