Slovenian President Borut Pahor | Khalil Mazraawi/AFP via Getty Images Slovenians push for EU constitution Document expresses concern about the EU’s future without the UK.

Senior figures in Slovenia, including President Borut Pahor, on Friday called for an EU constitution that aims to address "the serious decline in the European Union's size and strength following the exit of the United Kingdom."

The Ljubljana Initiative (which has the sub-heading "on the new constitutional process and new draft treaty establishing a new constitution for [the] European Union") calls for acknowledgement of the bloc's successes and expresses "serious concern" about a number of issues, including terrorism, migration and the financial crisis.

According to Pahor the idea is to “protect [the] European idea and build upon it in all its dimensions,” local press agency STA reported.

“We want EU to be a non-state federation, based on the values of constitutional democracy and that will serve to maintain the member states and strengthen our European values at the same time,”Matej Avbelj, professor of European law at the New University in Ljubljana and one of the c0-signatories, said.