"We have requested China to immediately clarify the new fisheries law issued by the Hainan Provincial People's Congress," the Filipino foreign department said in a statement.
"We are gravely concerned by this new regulation that would require foreign fishing vessels to obtain approval from Chinese regional authorities before fishing or surveying in a large portion of the South China Sea."
Press reports said the law was passed last year and took effect on January 1.
China claims almost all the South China Sea but the Philippines, Vietnam, Malaysia, Brunei and Taiwan have overlapping claims.
Tensions between the Philippines and China have risen in recent years as Beijing becomes more aggressive in asserting its claims.
Earlier this year Manila took Beijing to a United Nations tribunal over the contested Scarborough Shoal, which has been controlled by Chinese government vessels since last year.
"This new law reinforces China's expansive claim under the 9-dash line," the Philippine foreign department alleged Friday, referring to China's delineation of the extent of its maritime territorial claim.
"It is a gross violation of international law," the statement added.
"This development escalates tensions, unnecessarily complicates the situation in the South China Sea, and threatens the peace and stability of the region."
The statement said the Philippines was not the only country to be affected by the new Hainan regulations.
"These regulations seriously violate the freedom of navigation and the right to fish of all states in the high seas, as provided for under UNCLOS (the UN Convention on the Law of the Sea)," it said.
"Under customary international law, no state can subject the high seas to its sovereignty."