Vietnam on Friday rejected a US proposal to establish new trade rules for state-owned companies, which Washington says often benefit from unfair subsidies and protections.
The United States floated its plan in negotiations this week on the nine-country Trans-Pacific Partnership, or TPP, a free-trade zone that would stretch across much of the Pacific Rim.
"We don't think there is a need for specific provisions for state-owned enterprises," Vietnam's trade negotiator, Tran Quoc Khanh, told reporters.
He said Vietnam's state-owned companies already complied with World Trade Organization rules, so the US proposal was not necessary.
Despite the disagreement, President Barack Obama and leaders of the eight other TPP countries are expected to announce next month in Hawaii they are committed to finishing the talks and have the "broad outlines" of a final deal. It could take as much as another year to conclude the ambitious negotiations.
Obama is hosting the annual summit of the 21-member Asia-Pacific Economic Cooperation forum. All the TPP countries are also members of APEC.
Washington wants strong rules on state-owned enterprises in the TPP partly because the pact could become the foundation for future trade talks with China, a country with more than 20,000 state-owned companies.
A study conducted for the US-China Economic and Security Review Commission by the Washington consulting firm Capital Trade Inc said firms under various forms of Chinese state ownership controlled 50 percent of China's economy -- with huge impact on economic policy and trade.
Malaysia, another country in the TPP talks that has state companies, said it wanted to study the US offer further before staking out a position.
US negotiator Barbara Weisel said the proposal was drawn up after consulting with the business community and labor unions, which feel strongly that state-owned enterprises enjoy unfair support.
The United States for the first time this week also outlined its ideas on protecting workers' rights, another potentially contentious area of negotiation.
Delegates from the nine TPP countries -- Peru, Chile, Australia, Brunei, Malaysia, New Zealand, Singapore, the United States and Vietnam -- said they made significant progress in Lima in other areas but that sticking points remained, especially rules for intellectual property rights and market access.
"The US and other negotiating teams will return to their respective capitals and update their ministers on the specific outcomes of their work over the nine negotiating rounds, in preparation for assessment by the nine leaders at the APEC meeting," US officials said in a statement.