Labour leader Jeremy Corbyn has warned of "massive dislocation and job losses" at companies like Nissan, Airbus, BMW and Rolls-Royce if Brexit disrupts the cross-Europe supply chains which they rely on.
Airbus in Broughton, Flintshire employs around 6,000 people.
Corbyn is to have an "extended meeting" with the EU's chief Brexit negotiator Michel Barnier in Brussels next week.
The move is likely to be seen as an indication that Mr Corbyn wants the EU to be in a position to deal with Labour if there is a change of power in Westminster during the two-year Brexit negotiation process.
Earlier today the European Commission's chief negotiator warned it will not be possible for Britain to enjoy all the benefits of the single market or frictionless trade with its former EU partners after Brexit.
Mr Barnier said that Brexit would create a "loser/loser situation" for both the EU and UK, which would be worsened if the two sides failed to reach a deal.
Businesses, like Airbus in which rely on integration with continental Europe will face new "constraints" in moving parts and staff between centres of production.
Katherine Bennett, senior vice-president at Airbus UK, said there would be "ways around these challenges that may be coming up as part of Brexit".
She told BBC Radio 4's World At One: "It's really important that we work really closely with Michel Barnier and the UK Government to ensure that the customs issues which will arise can be dealt with and managed."