Fifteen countries presented Secretary-General Kofi Annan with a legal memorandum and a draft resolution backing UN membership for Taiwan, Gambian Ambassador Crispin Grey-Johnson told Reuters on Wednesday.
The issue will come up next month during preparations for the September 16 opening of the next session of the 191-nation General Assembly.
For Taiwan's membership to be considered, the assembly's General Committee - a panel on which every UN member has a seat - would have to adopt a resolution adding the issue to the agenda for the new session.
Taiwan is a bit larger than Belgium, has a population of more than 23 million people and is one of the world's largest economies.
Taiwan uses its economic clout to woo support from mostly tiny and impoverished UN members in Central America, Africa and the South Pacific.
But China has been even more forceful in making the issue a test of friendship. Along with most countries, China views Taiwan as a breakaway province, and insists it must be brought under its rule.
The UN membership question has raged since 1949, when Chiang Kai-shek's Nationalist government lost a civil war to the Chinese Communists but held on to China's UN seat even after fleeing to Taiwan.
In 1971, the General Assembly expelled Taiwan and gave the seat to Beijing. Most UN members now see Taiwan as part of a single China.
But Taiwan has argued that it should have its own seat in the world body in order to take part in the work of international organizations.