WATCH: Jill Biden speaks in front of flag partially inspired by Nazis

First Lady Jill Biden spoke before the United Farm Workers on Wednesday with union's flag in the background behind her to commemorate the birthday of Cesar Chavez.

The United Farm Workers is a union founded by the left-wing workers' rights activist Cesar Chavez in 1962. The union represents over 10,000 agricultural workers across the United States and is one of the defining achievements of Chavez's career. Chavez's legacy has been praised by the Biden administration, with President Joe Biden keeping a bust of the activist in the Oval Office.

However, some were quick to criticize the imagery behind the First Lady, noting that the flag was in part inspired by Nazi vexillology.

According to Smithsonian Magazine, "[the] story of the black eagle, the movement's symbol, exemplifies Chavez's skill as a tactician. He researched emblems, including cigarette boxes and Nazi flags, and concluded that the most potent color combination was red, black and white."

The flag does bear a striking resemblance to banners used by the Nazis. The Nazi German flag included a red background with a white circle and a black design within the circle. The Nazi flag put the circle off to the side rather than in the direct centre of the flag, and the symbol was a swastika rather than an eagle.

While the eagle is a commonly used symbol in Nazi iconography, the eagle on the Nazi flag is the Reichsadler, also known as the Imperial Eagle, while the one used by the UFW is a Mexican eagle.

Defenders of the flag have argued that the Nazi behind the flag is indirect, and that the colour scheme was simply used to be eye-catching rather than to associate the movement with the Nazis.

Chavez himself was a political leftist who compared himself to the Viet Cong, a communist guerilla organization which fought against American forced in Vietnam. He also took heavy inspiration from his Roman Catholic upbringing, and frequently used Catholic imagery and symbolism in his activism.

In his lifetime, Chavez was often accused of being a communist. An FBI investigation into such leanings found no evidence of communist orientation, and more left-wing members of his movement have often criticized him for allying with anti-communists and for conducting purges of his union under the guise of rooting out communists.