Whitsun Reef, also known as Whitson Reef, Whitsum Reef, and Julian Felipe Reef (Tagalog: Bahura ng Julian Felipe; Mandarin Chinese: 牛轭礁; pinyin: Niú è jiāo; Vietnamese: Đá Ba Đầu), is a reef at the northeast extreme limit of the Union Banks in the Spratly Islands of the South China Sea. It is the largest reef of the Union Banks.