President Yoon Suk Yeol, right, speaks with doctors during a visit to a hospital in Bucheon, west of Seoul, on April 9. (Yonhap)

The South Korean opposition's landslide victory in the latest parliamentary elections is likely to upend the conservative ruling party's push for key proposals and initiatives, observers said Sunday.

One of the ideas that the ruling People Power Party had vowed to pursue, administratively merging Gyeonggi Province's Gimpo city into Seoul, otherwise known as the so-called “Megacity Seoul" project, could be scrapped, an expert said.

“Discussion on the Megacity project is likely to be scrapped (now),” said Shin Yul, a political science professor at Myongji University in Seoul.

“Momentum (for the project) could be revived ahead of the upcoming 2026 local elections, but the buzz surrounding it won’t be at the level it was ahead of the latest parliamentary election,” he noted.

In November last year, the ruling party proposed a special bill aimed at incorporating Gimpo -- population 486,000 -- into Seoul. Other cities were not included in the bill, but the ruling party had announced separate plans to merge parts of other key metropolitan areas such as the southern city of Busan with nearby areas.

In the months leading up to the election, the ruling party had pushed for the project, with former People Power Party interim leader Han Dong-hoon even visiting Gimpo in early February in an attempt to attract voters in the area. Critics, meanwhile, accused the project of being a populist pledge, labeling it an attempt to lure Gimpo voters seeking a boost in their property value.

Despite this campaign, candidates from the main opposition Democratic Party of Korea won both of Gimpo's constituencies in last week's election, reflecting voters' distrust and even disinterest in the ruling party's proposal.

The Megacity Seoul bill is set to take effect on Jan. 1, 2025 -- if it is passed at the National Assembly.

Several other government initiatives are projected to face roadblocks now as well, including a plan to relax real estate regulations to fuel the redevelopment of older apartments across the country. The plan includes adopting a relaxed safety review yardstick for apartments over 30 years old for reconstruction and reducing taxes on owners of multiple properties.

The opposition has opposed the Yoon administration’s real estate plans, calling them initiatives that will “only benefit the rich.”

“The current administration’s policy goals aim to either alleviate or scrap the previous (liberal Moon Jae-in administration’s) policies. The rival parties are projected to clash at the National Assembly over the Yoon administration’s new plans,” Lee Eun-hyung, a researcher at the Korea Construction Policy Institute, said.

Yoon's plan to scrap the implementation of the financial income tax system, scheduled for Jan. 1 next year, faces a rocky road. The system aims to levy a 20 percent tax on investors who earned capital gains of over 50 million won ($38,000) from stock investments, while those who earned over 300 million won will be subjected to a 25 percent tax.

The main opposition has called for the scheduled implementation of the taxation, which has already been delayed for two years, claiming that a possible scrap could result in a loss of an annual 1.5 trillion won in taxation.

Meanwhile, the opposition bloc is likely to work towards passing a special investigation bill for a probe into suspicions that the government and the police exerted influence in delaying the investigations into the death of a young marine. Marine Cpl.

Chae Su-geun was swept away by a current near the country's central region of Yecheon County on July 19 last year while on a search and rescue mission for flood victims. It is suspected that Chae was forced by his superiors to participate in the risky rescue operation without proper safety measures.

The main opposition Democratic Party and its satellite party secured a total of 175 seats, with other opposition parties winning 17 seats. Meanwhile, the ruling People Power Party and its satellite party only won 108 seats in the single-chamber, 300-seat National Assembly, according to the National Election Commission on Thursday.

The outcome of the election is likely to impede the conservative Yoon administration’s plans and make Yoon himself a lame duck for his remaining three years in office, observers noted.