Aeroports de Paris (ADP), Fraport and Manchester Airports Group (MAG) have challenged the tender award to manage Sofia International Airport in Bulgaria.

The three losing suitors have appealed to the Bulgarian Transport Ministry to reconsider its decision to grant the 35-year concession to French-German consortium SOF Connect, which operates Munich Airport.

The consortium of ADP, Fraport, and MAG had proposed the highest concession fee to operate Sofia Airport in Bulgaria after the Transport Ministry opened bids in May.

It offered to pay €32.8m per year, or 42.8% of the annual revenue if it was higher.

In addition to the annual concession fee, ADP offered to invest €903m in Sofia Airport over the duration of the contract.

ADP filed its complaint with Bulgaria’s Commission for Protection of Competition, the anti-monopoly regulator said on its website.

The UK’s MAG, which placed its bids in collaboration with Chinese construction firm BCEG, has also appealed, along with the consortium led by SSB Sauernwein & Schaefer.

The winning consortium agreed to pay an annual concession fee of €24.5m ($27.23m), or 32% of annual revenues. It also committed to spending €608m on Sofia Airport.

Bulgaria’s Transport Ministry said that it made the decision following an assessment of the reliability and sustainability of the business and financial models for the airport’s development.

Once the new terminal becomes operational, there are plans to convert Terminal 1 into a cargo-only facility.

The airport handled seven million passengers last year.

Austria-based construction firm Strabag, which also built Sofia Airport’s Terminal 2, is expected to take up the construction work at the airport.