UPDATE:
A Lufthansa official says:

“These figures only represent the volume of bookings made though the GTMC channels and do not take account of increases in the bookings through other avenues. The fact is that we have sold more tickets online via our own online channel LH.com where the share has risen from 29% in June 2015 to 35% in December 2015."
"Looking at bookings across the Lufthansa Group we cannot see any decrease due to the introduction of the DCC on September 1, 2015. As published in our Q3 results, the Lufthansa Group is heading towards a record in 2015. The published traffic figures for the later months of 2015 were influenced by the biggest and longest strike action in the Lufthansa history.
"Even taking this into account, we cannot see any switch away from Lufthansa."
ORIGINAL:
Lufthansa has lost 8.5% market share due to its "flawed and failed strategy" to add a surcharge to bookings via Global Distribution Systems.
That's the claim by the Guild of Travel Management Companies, after having compared data for the three months before and after the Euro 16 fee was added to fares on the carrier made through Travelport, Sabre and Amadeus.
The organisation says around 12,000 transactions were monitored at UK-based travel management companies to gauge if the introduction of the charge on September 1 last year had made any difference to the booking strategy of corporate travel agencies.
The GTMC says TMCs have switched business away from the airline group to avoid passing on the fee to travellers.
It also claims that Lufthansa's market share was 32.9% in June this year, with it falling to 24.4% by November.
Beneficiaries have been other airlines, such as EasyJet, although British Airways was flat.
The GTMC does not mention that the Luthansa Airline Group had two significant periods of industrial action between September and November.
Lufthansa has previously claimed drops in traffic via GDSs were the fault of the series of strikes.
GTMC CEO Paul Wait says:

"We predicted that the Lufthansa charge would upset and put business travel bookers off. They haven’t booked directly with Lufthansa as they hoped, instead, they have voted with their feet and taken their business elsewhere.
"In this highly competitive market, we believe, this charge has done some obvious damage to Lufthansa’s market share."
A highly confidential document circulating amongst the top brass at Sabre Travel Network, obtained by Tnooz from a third party in September last year, shared official booking volumes for all Global Distribution Systems and outlined how Lufthansa Group bookings in Europe in the first two weeks of September are said to be down 16.1% year-on-year versus a flat year-to-date up to August.
It also reported that on routes where Lufthansa has a market share of 30%-60%, volume drops of up to 30% were experienced in the first week of September. Competitor carriers British Airways, Air Berlin and Air France were said to gaining as a result from the declines.