More than three-quarters of U.K. public companies surveyed by an auditors’ group haven’t discussed contingency planning for the nation’s potential exit from the European Union with the chairman or the head of the board’s audit committee.

Over 60 percent of the surveyed companies intend to make contingency plans for the possibility of a so-called Brexit but said it isn’t yet possible to do so, the Chartered Institute of Internal Auditors said Friday in a statement. The group surveyed heads of internal audit at FTSE 250 organizations, with 39 submitting feedback. The institute said 77 percent of executives rated Brexit as a more significant risk now than it was six months ago.

“Most boards haven’t undertaken contingency planning yet, but most plan to,” said Ian Peters, the chief executive of the institute. “The challenge is that uncertainties about what Brexit may mean are making planning very difficult at the moment.”

With the U.K. referendum on its EU membership just over two months away, the increased uncertainty may already be affecting confidence among executives as well as companies’ willingness to borrow, invest and hire, the Bank of England said on Thursday. Opinion polls suggest Britons remain undecided as to whether to remain in the EU ahead of the June 23 vote.

Prime Minister David Cameron is campaigning for the U.K. to remain in the EU, with U.S. President Barack Obama set to join the debate with a clear call against a Brexit next week. A U.K. exit from the EU would cause “severe” damage to the world economy, International Monetary Fund Managing Director Christine Lagarde said on Tuesday.

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