The European Commission has launched an investigation into whether O2 and T-Mobile Czech Republic's network sharing programme is harming the country's telecoms market.
Both operators account for around three quarters of the Czech market, with Vodafone the third operator. After O2 spun off its mobile infrastructure and wholesale arm into a standalone company called CETIN, both telcos began network sharing in 2011.
The combined network includes 2G, 3G and LTE infrastructure and covers the entirety of the Czech Republic, aside from the capital, Prague, and the city of Brno.
In a statement, the Commission said it wanted to see if the network sharing programme had led to a slowdown in improving existing hardware, and the delay in deploying new technologies and services, especially in densely populated areas.
It added that the launch of an investigation does not prejudice the outcome of it. There is no deadline for when the findings of the investigation will be revealed.
EU Commissioner in charge of competition policy Margrethe Vestager said: "Network sharing agreements can bring about efficiencies, such as reduced deployment costs and may allow for network expansion to previously unserved areas. But, in some circumstances, network sharing may also reduce competition on the market.
"The network sharing agreement between the two major operators in the Czech Republic covers most of the country. We need to ensure that it will not reduce infrastructure competition and innovation.”
Earlier this year, French regulator Arcep said network sharing needed to be restricted or else competition would be harmed. There are two such programmes in France, between Free Mobile and Orange, and SFR and Bouygues.