The City of Helsinki has been investigating congestion charging for several years.
There is a comprehensive study: Helsinki Region Congestion Charging Study undertaken in 2009. And another study: Helsinki region congestion charges. Follow-up study (see summary here) which was released by a Finnish central government working group in 2010.
The current conclusion is that a Helsinki congestion charge could reduce congestion, improve traffic safety, reduce air pollution and increase patronage of public transport. The potential is there as Helsinki has an excellent metro, suburban rail, tram and bus network, and a downtown bounded by a major ring motorway and water.
The main reasons opposing a congestion charge are:
-The insufficient public transport capacity and lacking funds to improve it
-The high cost of retrofitting vehicles with On Board Units
No final decision has been made yet.