I think it’s A.F. of L. which was the American Federation of Labor, formed in 1886 in Columbus, Ohio by the diehard capitalist Samuel Gompers. The Federation was a collective of smaller craft unions such as the masons' union, the hatmakers' union and Gompers's own cigarmakers' union (he was from a family of Jewish cigar-makers, formerly resident in London).
These unions exclude unskilled workers and the collective wielded its power to raise wages for those in skilled trades by collective bargaining, using strikes and boycotts where necessary. Gompers himself strongly opposed socialism, spread racist arguments about the inferiority of Chinese immigrant workers, but maintained government support by shunning any drive for radical political change. During WWI he openly supported the war effort and did his best to raise worker morale (and wages), avoiding disruption from strikes.
The Federation was the most active national labor organization until the Great Depression when unskilled workers finally came together and ultimately merged with the Congress of Industrial Organizations in 1955 to become AFL-CIO.
Presumably the ‘Juniors’ were a subset of the Federation.