The plan was presented by the UN envoy for Kosovo, Martti Ahtisaari.
Tadic issued a statement after their meeting in Belgrade, saying he had told the Finnish diplomat that Serbia and he as its president would never accept Kosovo's independence.
"The imposed independence of Kosovo would be in contravention of the basic principles of international law and would set a very dangerous political and legal precedent," the Serbian president said in his statement.
Tadic said that the proposal did not explicitly mention the independence of Kosovo, but that neither was there any mention of Serbia's sovereignty and territorial integrity over the province.
"Because of this fact and some other provisions, Ahtisaari's plan opens up a possibility for the independence of Kosovo and Metohija," the statement says.
A new Serbian Assembly has not yet been inaugurated after the January 21 election and negotiations are under way to form a new government. Tadic announced consultations with parliamentary parties in the coming days in an effort to find a way of defending Serbian national interests and enforcing government policy on Kosovo, which had received unanimous support in the Assembly.
The Serbian Foreign Ministry also issued a statement on Friday, saying that by proposing independence for Kosovo Ahtisaari had overstepped the authority granted to him by the UN Secretary-General and the Security Council because he transformed the negotiations on the status of Kosovo into a change of the status of the internationally recognised state of Serbia as one of the founders of the United Nations.
Ahtisaari's plan dramatically changes the borders of the state of Serbia by force and against its will and in violation of the UN Charter, the statement said.
The Foreign Ministry said it would inform the big-power Contact Group for Kosovo, the UN Security Council, the European Union and NATO about Ahtisaari's overstepping of authority, adding that it would be as constructive as possible towards any proposal for the Kosovo status that did not threaten the territorial integrity of Serbia.
Serbian Prime Minister Vojislav Kostunica refused to meet the UN envoy, saying that his plan was "illegitimate" and contrary to the UN Charter and international law.
Speaking to reporters after meeting Tadic, Ahtisaari said he hoped Kosovo's status would be defined by spring, by which time Belgrade and Pristina were supposed to present their objections to his proposal. He declined to comment on the possibility of Kosovo eventually becoming independent.