Following a barrage of criticism on Tuesday from the American Chamber of Commerce in Ireland, lobby group IBEC and State agency Shannon Development, of the Aer Lingus decision to end its Shannon-London Heathrow daily service later this year, industry executives from the foreign-owned sector continued to pile on the pressure on Wednesday.

The general manager of Element Six, which distributes man made diamonds globally from Shannon, has said the company's 600 employees face a very uncertain future if a replacement carrier or route isn't found before the Aer Lingus service is withdrawn.

Element Six, which was formerly De Beers Industrial Diamonds, has been located in Shannon for the last 45 years.

Ken Sullivan is General Manager of Element Six in Shannon and told RTE News that some of the jobs at the company are under threat.

He is reported to have said that the rationale for the operation remaining in Shannon was challenged, without a local air service to Heathrow as in common with many companies in the region, Element Six is part of a much wider group who've set up in the Shannon on the assumption their customers could easily get to them and their executives could easily connect with the rest of the world.

The common denominator for all that was easy access to Heathrow on what the region's business understood to be a profitable and secure Aer Lingus service.

Also,  Shannon based IT company Avocent, told RTE News that the Aer Lingus withdrawal will make it much more difficult to pitch for new investment from company headquarters in Alabama.

Both Avocent and Element Six have been building their employment presence in Shannon. Both say 90% of their customers connect via Heathrow to visit their facilities.