▁War ▁I ▁w art ime ▁indust ries ▁to ▁pe ac etime ▁construction ▁caused ▁considerable ▁difficulties . ▁Jur is dict ional ▁problems ▁also ▁developed ▁with ▁other ▁national ▁Un ions , ▁but ▁the ▁United ▁Association ▁retained ▁juris diction ▁over ▁important , ▁growing ▁areas ▁of ▁work ▁like ▁construction ▁of ▁industrial ▁plants , ▁public ▁util ities , ▁pet role um ▁facilities ▁and ▁resident ial ▁buildings . ▁ ▁In ▁the ▁first ▁half ▁of ▁the ▁century , ▁the ▁United ▁Association ▁moved ▁to ▁formal ize ▁app rent ices hip ▁training ▁programs , ▁including ▁making ▁a ▁five - year ▁app rent ices hip ▁mand atory ▁in ▁ 1 9 2 1 , ▁and ▁in ▁ 1 9 3 8 ▁holding ▁that ▁all ▁app rent ices ▁be ▁members ▁of ▁the ▁United ▁Association ▁and ▁attend ▁related ▁training ▁classes . ▁Its ▁National ▁Pl umb ing ▁App rent ices hip ▁Plan ▁of ▁ 1 9 3 6 ▁was ▁the ▁first ▁set ▁of ▁standards ▁gover ning ▁app rent ices hip ▁to ▁win ▁appro val ▁of ▁the ▁federal ▁government . ▁ ▁In ▁the ▁De pression , ▁United ▁Association ▁membership ▁fell ▁from ▁its ▁ 1 9 2 9 ▁peak ▁of ▁ 6 0 , 0 0 0 ▁to ▁ 2 6 , 0 0 0 ▁by ▁ 1 9 3 3 . ▁ ▁After ▁several ▁constitution al ▁changes ▁through ▁the ▁years , ▁the ▁ 1 9 4 6 ▁convention ▁changed ▁the ▁name ▁of ▁the ▁organization ▁to ▁its ▁present ▁name : ▁The ▁United ▁Association ▁of ▁J our ne ymen ▁and ▁App rent ices ▁of ▁the ▁Pl umb ing ▁and