The contractors are desperately worried that a case currently before the court, Ayse Suzen v Zehnacker Gebaude Reinigung GmbH Krankenhausservice, will ultimately allow rivals to ignore TUPE and so undercut them and DSOs by bearing down on labour costs.
Under the umbrella of the Public Contractors Association, the firms - including CCT heavyweights such as CSL, Onyx, PSec and SITA - have written to all MPs, MEPs, council chief executives and secretaries of the local authority associations to make their support for TUPE known.
PCA secretary Cliff Davis-Coleman said DSOs and companies had inherited significant liabilities in short-term contracts and predicted job losses unless TUPE remains.
Mr La Pergola ruled: 'It is unjustifiable that the operator, on whom the contract was conferred, should be obliged to retain the personnel who previously provided the service.
'There is no relationship between the two undertakings who provided the service.'
The advocate general's opinion is likely to heavily influence the court's final ruling, which is expected within the next two months.
But the contractors insist the Suzen opinion is 'fundamentally flawed' and want all political parties and contracting public bodies to state their support for TUPE.
The PCA also called on matters of employment law interpretation to be left to EU member states and so covered by the principle of subsidiarity. It fears the court has failed to recognise the 'unique' circumstances in the UK created by CCT.
Association of Metropolitan Authorities secretary Rodney Brooke said he welcomed the fact that the contractors now recognised the value of TUPE, the removal of which would 'throw a huge spanner in the works'.