Five Philippine congressmen are set to visit the disputed Spratly islands on Wednesday, reigniting a territorial row in the South China Sea.
China has said the planned trip by the lawmakers could damage bilateral ties. China and the Philippines are among six nations which claim the islands.
Earlier Indonesia’s president said nations should agree a code of conduct for disputes in the South China Sea.
Ministers were at an Association of South East Asian Nations summit.
Susilo Bambang Yudhoyono addressed representatives as they gathered in Bali for talks with a particular focus on disputes over parts of the South China Sea.
China, Vietnam and Taiwan all claim sovereignty over huge areas of the sea, including the Paracel and Spratly island groups. The Philippines, Malaysia and Brunei also claim overlapping areas of territory.
The Spratly islands lie in the middle of the South China Sea, an area thought to be rich in oil and gas. The region also has vital shipping routes.
The five Philippine members of parliament are visiting Pagasa, the largest of the island chain under Philippine control.
According to one of the congressmen, Walden Bello, this is a private trip to meet residents and soldiers stationed there and to support the territorial claims of the Philippines.
But the Chinese embassy in the he Philippines said the trip “serves no purpose but to undermine peace and stability in the region and sabotage the China-Philippines relationship.”
“There is no reason for the Chinese embassy to worry. They seem to be over-reacting to a very small, peaceful mission,” said Bello.
“We have every right as Filipino citizens to visit Philippine territory.”
The BBC’s Kate McGeown in Manila says that tensions have risen in recent months after the Philippines and Vietnam complained of Chinese incursions into what they see as their territorial waters.
The meeting in Bali culminates on Saturday with talks on regional security which will include China, Japan and the US.
But correspondents say that tensions over the sea are likely to overshadow the summit.