South Korea said on Sunday that the United States had proposed some revisions to a free trade agreement between the two countries, in areas including labor rights, environment and investment.

The two had planned to sign the agreement, the biggest U.S. trade pact in 15 years, on June 30 in Washington. The initial agreement came in April after nine months of negotiations and despite protests from South Korean farmers fearing a flood of cheaper U.S. farm products.

Many U.S. lawmakers from auto producing states charged the agreement would give South Korea a one-sided advantage to export more cars to the United States.

Seoul's foreign ministry said in a statement released late on Saturday that the U.S. Trade Representative's office hoped to have additional discussion next week over the proposals.

One phase of the proposals, according to the ministry's statement, suggests the trade pact state that no non-U.S. investors in the United States will be given preferential treatment over U.S. investors.

The government will closely study the U.S. proposals and decide our next steps after coordination among government offices, the foreign ministry said.