All appeals are dismissed.

The request for taking over a lawsuit by the applicant is dismissed.

The costs of appeal are assessed against the defendant.

The grounds of appeal are examined (to the extent of supplement in case of supplemental appellate briefs not timely filed).

1. The reasoning of the lower judgment and the record reveal the following.

The Seoul Special Metropolitan City Urban Infrastructure Headquarters requested the Defendant to conclude a contract for the construction works C (hereinafter “instant construction works”) in the Republic of Korea.

Defendant Republic of Korea announced the announcement of the instant construction work on December 18, 2007.

The plaintiffs participated in bidding by organizing a joint supply and demand organization consisting of 7 companies including FF Co., Ltd. and Plaintiff A Co., Ltd., and the joint supply and demand organization was selected as qualified.

On May 30, 2008, the joint supply and demand company entered into a contract for the instant construction project in the amount of KRW 135,658,00,000 with the Defendant Republic of Korea for the total amount of construction works.

The contract amount includes health insurance premiums and national pension premiums (hereinafter referred to as "health insurance premiums, etc.") for workers belonging to the joint contractor.

Until September 30, 2015, the joint supply and demand company entered into a contract for construction of facilities with the defendant Seoul Special Metropolitan City and the defendant for the modification of the contract through six times.

On September 30, 2015, a joint supply and demand company completed the instant construction project, and finally entered into an additional contract with the Defendant Seoul Special Metropolitan City for the construction of the final facility that constitutes the contract amount of 159,748,000,000.

The contract amount is 1,189,781,00 won after the defendant Seoul Special Metropolitan City settled health insurance premiums, etc.

B. The Plaintiffs filed the instant lawsuit seeking the payment of the reduced construction cost on the grounds that Defendant Seoul Special Metropolitan City settled health insurance premiums, etc. without contractual or legal grounds.

2. Whether health insurance premiums can be settled pursuant to the Framework Act on the Construction Industry and the Enforcement Decree thereof (ground of appeal Nos. 1 and 2)

A. Article 22 of the former Framework Act on the Construction Industry (amended by Act No. 8477 of May 17, 2007) is a contract for construction work.