The United Front for Democracy Against Dictatorship (UDD), whose supporters are commonly called Red Shirts, is a political pressure group opposed to the People's Alliance for Democracy (PAD), the 2006 Thai coup d'état, and supporters of the coup. Notable UDD leaders include Jatuporn Prompan, Nattawut Saikua, Veera Musikapong, Jaran Ditapichai, and Weng Tojirakarn. The UDD allies itself with the Pheu Thai Party, which was deposed by the 2014 military coup. Before the July 2011 national elections, the UDD claimed that Abhisit Vejjajiva's government took power illegitimately, backed by the Thai Army and the judiciary. The UDD called for the Thai Parliament to be dissolved so that a general election could be held. UDD accused the country's extra-democratic elite—the military, judiciary, certain members of the privy council, and other unelected officials—of undermining democracy by interfering in politics. The UDD is composed of mostly rural citizens from northeast (Isan) and north Thailand, of urban lower classes from Bangkok, and of intellectuals. Although the movement seems to receive support from former prime minister-in-exile Thaksin Shinawatra, not all UDD members support the deposed prime minister.

The Red Shirts are a political movement in Thailand, formed following the 2006 coup d'état which deposed then-Prime Minister Thaksin Shinawatra. Originally synonymous with the United Front for Democracy Against Dictatorship (UDD), a group formed to protest the coup and resulting military government, the movement subsequently expanded to include various groups with diverse political priorities. Its members range from left-wing and/or liberal activists and academics to the large number of Thaksin's rural and working-class supporters. The movement emerged as the result of socio­economic changes in Northeast Thailand in the 1990s and 2000s, including a growing middle class, rising aspirations, and an increasing awareness of the extreme inequality and of the fundamentally weak democracy in Thailand, typified by Thailand's primate city problem. Red Shirts group dynamics center on frustrated economic and political aspirations to improve democracy and overcome inequality, which contributed to the 2009 Thai political unrest and the 2010 Thai political protests, as well as shared suffering at the hand of the ruling class hegemony. As with other minorities, the Red Shirts have been dehumanized and demonized, with insults such as "Red Buffalo", since reclaimed by some of its targets. Their claims for transitional justice following the 2010 Thai military crackdown have been subverted by the Thai state.