Unionized workers of Asiana Airlines reiterated Thursday their opposition to a merger with the nation’s largest air carrier Korean Air, expressing their intention to block further procedures by all means.

Asiana Airlines' labor unions urged the air carrier's main creditor Korea Development Bank and the European Commission, the EU's antitrust regulator which gave conditional approval on the merger, to review the deal from the ground up.

The possible future actions that Asiana Airlines' general labor union and pilots' labor union unions could take include the resignation of cargo flight attendants and accusing Asiana Airlines CEO Won Yoo-seok of breach of trust.

"We made countless attempts to meet with Korean Air's management to discuss the job security and the fair treatment of our employees, but they gave us no answers," Choi Do-sung, head of the pilots' union said during a press conference Thursday at the Korean Confederation of Trade Unions in central Seoul.

Choi argued that the recent selection of Air Incheon as the preferred bidder for selling Asiana Airlines' cargo business, which he called "a small cargo airline with no long-distance flight experience," is a scheme for Korean Air to take over the cargo sector.

Asiana Airlines' general union head Kwon Soo-jeong argued that the merger between the two companies would significantly damage the competitiveness of the nation's infrastructure industry.

"The creation of a 'mega-carrier,' which Korean Air claimed to be the merger's ultimate goal, was undermined by the return of countless slots and the sale of cargo business," Kwon said. "Slots require years of effort to be distributed as a key asset of airlines. But by giving up so many, it became a deal with more losses than gains."

Meanwhile, Craig Malcolm, chairman of the Associations of Star Alliance Pilots, was invited by the union to attend the conference in Seoul but was absent.

The association explained that while the ASAP supports the union’s statement, it is difficult for them to fully join because the airlines affiliated with Star Alliance aim for Korean Air's slots that might be returned in the event of the merger.