The protest is against Single European Sky (SES 2+) proposals to hive-off support services, such as engineering, from ATM services and outsource them.
But NATS' staff argue that support services like communication, navigation, surveillance and aeronautical information are an integral part of the core business provided by air navigation service providers like NATS. Separating the activities and subjecting them to artificial market conditions will affect safety standards and fragment service provision in a drive for profits.
The protest is part of a second day of action organised by the European Transport Federation. Members of affiliated ATM unions will take part in walkouts, rallies, meetings, protests and strikes across Europe.
The aim of SES is to improve air traffic services through legislation, technology, new practices and airspace changes, moving to functional blocks rather than national borders.
But under the latest proposals - SES 2+ - the European Commission, which sets the legislation, wants to link the plans to stringent performance targets designed to halve ATM costs by 2020. Unions say this will result in the widespread job losses.
The UK's ATM unions believe that mandatory centralising and outsourcing of support services will result in a poorer service to airlines and increased conflict between cost and safety.
Prospect National Secretary Emily Boase said: "Subjecting safety critical services to market conditions in a drive for economic returns is a step too far. Providers would not even have the choice about which services would have to be undertaken by other companies – the legislation will require them to cease providing such services themselves. Unbundling support services will create more interfaces that will require a greater degree of management, introduce inefficiencies and increase costs.
"Our members, and colleagues across Europe, are concerned that separating air navigation from other air traffic services will break the safety chain and lead to a breakdown in accountability, as we have seen previously in the railway industry."
PCS National Officer Jeremy Gautrey added: "This draft legislation is widely discredited by staff working in the ATM industry, many national ATM providers and many European member states.
"The commission has so far failed to listen to those working in ATM. The action taken by unions affiliated to the ETF on 30 January risks causing significant industrial unrest across the whole of Europe and could be avoided if the commission listens.
"The UK and Europe provide excellent ATM services and while we support improvement, it must not be at the expense of jobs and safety. The UK's safety record and service is one of the best in Europe and this could be jeopardised by this ill-thought through legislation which, so far, has attracted little support."
Prospect represents 3,000 people working as controllers, systems engineers, scientists and specialists. PCS represents 1,000 NATS operational, managerial and support staff. Both unions are affiliated to the European Transport Federation.