In 1919, Benito Mussolini united various groups in the then Kingdom of Italy to form the Fasci di combattimento. During the Biennio rosso (1919-1921), the Black Shirts used targeted terror against striking industrial workers, the Partito Socialista Italiano (PSI) and all opposition. As a result, local and regional anti-fascist groups as well as vigilante groups emerged from 1920 onwards, encompassing the entire political spectrum, from Catholics and liberals to socialists and anarchists.

Emphasis by me

In 1921, Mussolini transformed his militia movement into the National Fascist Party. The first armed anti-fascist organization came into being in 1921 with the Arditi del Popolo. It was open to anarchists, communists, social democrats, Christians and bourgeois republicans. However, the leadership of the PSI and the Partito Comunista Italiano (PCI) rejected the League. It remained limited to a few thousand members and a few cities.[3] This was the first organization with an explicitly anti-fascist self-image. Its supporters referred to themselves as antifascisti[4].

Emphasis by me

Arditi del Popolo

It grouped revolutionary trade-unionists, socialists, communists, anarchists, republicans, anti-capitalists, as well as some former military officers

Composed of Italian anarchists, socialists, and communists, the Arditi del Popolo were not supported by leftist parties (neither by the Italian Socialist Party, PSI, nor by the Communist Party of Italy, PCd'I).

Furthermore, the PCd'I ordered its members to quit the organization because of the presence of non-communists in its ranks.[8] The PCd'I organized by themselves some militant groups (the Squadre comuniste d'azione), but their actions were relatively minor and the party kept a non-violent, legalist strategy.

The Antifaschistische Aktion grew in the soil of the SPD and KPD in Nazi Germany (which themselves where not autoritarians or tankies at the time), but it's roots are older, decidedly anti-authoritarian and open to the entire political spectrum that wanted to fight fascism.

Edit: Antifascism is represented by a red and a black flag. How you could ever think is has anything to do with the authoritarian left when it's roots are so extremely anarchist is beyond me.