Ernst specialises in Netherlands tax treaties and tax legislation. He focuses on resolving (major) disputes between tax payer and tax administration, international mutual agreement procedures. He uses his past experience and contacts.
From 1973 he has worked for the Dutch Ministry of Finance, advising the (deputy) Minister of Finance on tax policy and legislation. The longest period of time he has negotiated for the Netherlands tax treaties and some EU-directives. He has represented the Netherlands in of the OECD meetings in Paris, lastly in the OECD project (1998) on Harmful Tax Competition. He has also been a member of the Dutch delegation in the European Code of Conduct Group.
From mid 1999 Ernst has been responsible in the Dutch Tax Administration for (the organisation of) the levying of tax from large enterprises in the Netherlands, including the ruling team.