He said: 'So many companies can hire cheap labour from abroad such as Eastern Europe, how can other construction companies possibly compete?
'We also want to see an improvement in health and safety standards. These sorts of issues could all be dealt with at the procurement stage.'
But construction minister Alun Michael was unable to confirm any changes in Government procurement policy at the Construction Confederation-sponsored event.
He said: 'The public sector client is not just one individual and that is why it is so hard in terms of procurement.'
Confederation chairman Peter Commins said: 'With the Government as one of the main clients -
dealing with over 40 per cent of the UK construction work - something needs to be done by them.'
The European Commission's Services Directive would allow contractors to adopt the standards of countries in which they are based, rather than of those they supply to.
Union leaders fear firms could set up branches in Eastern Europe and supply workers back to the UK, allowing them to pay lower rates.
Mr Ritchie said: 'The directive as it stands will force down contractors' prices because they would have to compete with companies technically based in countries with lower wages, lower social charges and little regulation. This will inevitably undermine the pay and conditions of building workers in the UK, Germany and other developed nations.
'The prices from proxy companies set up in Eastern Europe will always undercut those of companies based in Britain.'