A limited liability company must file a franchise and excise tax return even if it chooses to be ignored as an entity for federal tax purposes and is treated as an individual taxpayer or as a "division" of a general partnership federally. The law specifically says that limited liability companies are subject to tax, by including them in the definition of "taxpayer" or "person." Therefore, unless a particular limited liability company falls within an exemption contained in the law (see Tenn. Code Ann. Section 67-4-2008), it is taxable.
Reference: Tenn. Code Ann. § 67-4-2004(38).