The plans put in place by Europe for a no-deal Brexit "fall short of what is needed to limit major disruptions", business lobby groups have said.
In a letter seen by BBC's Newsnight, Business Europe, an umbrella group for lobby groups across the EU, including the UK's CBI, warned the European Commission of flight disruption, problems with data sharing and the short supply of drugs and medicines.
The Commission said it was holding frequent conversations with stakeholders across Europe. While much has been made about the UK preparations for a no-deal, the letter suggests that European businesses are very nervous about the implications of a no-deal.
Earlier in March, Michel Barnier, the EU's chief Brexit negotiator, said: "The risk of a no deal has never been higher... we are ready."
However, the CBI's head of EU negotiations, Nicole Sykes, told Newsnight: "No one is ready - not the UK, not the EU."
Currently, the UK is due to leave the EU without a deal on 29 March. On Thursday, EU leaders agreed to extend the Article 50 deadline until 22 May, but only if MPs agrees to the Withdrawal Agreement deal agreed by Theresa May. If there is no support for the deal, the EU is willing to extend the deadline until 12 April, where the UK must set out its plan to move forward or leave without a deal.
The letter sent to the European Commission was highly critical of the Contingency Action Plan it published in December. Business Europe claims measures taken "may not be enough to prevent disruptions in the European aviation sector", and that there is a "disjointed approach" to the certification of medical devices.
It argues a lack of "capacity" to change the structure of corporate data flows will significantly impact the flow of cross-border services. The letter also claims that authorisation of drug imports to the UK will need to be passed to the EU, which is likely to cause supply shortages.
The European Commission said: "We can confirm receipt of this letter and we will reply in due course. We are frequently in contact with stakeholders, including Business Europe."