The Korea Rail Network Authority, which manages the KTX bullet train railway tracks, is under fire for having allegedly provided ``special favors'' to an unqualified subcontractor for its Gyeongbu High-speed Line construction.

About 330 concrete railway sleepers on the 96.9 kilometer-long railway line linking Daegu and Ulsan were found to be cracked last month, according to an investigation by a committee of the National Assembly.

The committee said the sleepers absorbed water from rainfall in the summer through faulty sleeper ties attaching the rails to them. The water then froze in the winter and expanded, cracking the ties.

The network authority chose Cheonwon RailOne, a subsidiary of German company RailOne that designed the railway. The sleeper ties the Cheonwon RailOne supplied were found to be substandard because they used sponges to absorb moisture instead of a special waterproof material to repel it.

The faulty ties are raising questions as to whether there were any under-the-table deals in the selection procedure.

A field inspection team also failed to detect the problem in the first place and magnified the problem, according to officials from the construction ministry and opposition party members.

The Gyeongbu High-speed Line, a 254.2 kilometer-long track linking Daegu and Busan, is due to open in December next year, but observers say all 153,000 sleeper ties used in the construction should be replaced, costing an extra 13 billion won ($10 million) and delaying the scheduled opening.

The network authority said there would not be a delay. ``We are sorry for the mishaps but we will put everything back on track by the first half of the year,'' a network spokesman said.