To be honest, we would have to acknowledge that much of the construction industry that the labor unions serve is influenced by those in organized crime. So, yes, probably the 1975 disappearance of Jimmy Hoffa had to do with the actions of rival labor unions and their connections with the Mafia.
Yes, Jimmy Hoffa's 1975 kidnapping/disappearance was caused by rival labor unions, because he had too much power. The labor unions are kind of like the mafia. If one of them has too much power, other unions will not want that person around so that they can get more power for themselves.
The idea that Jimmy Hoffa, who made many enemies during his time, was kidnapped by rival labor unions is an interestingn one. I do not find it to be a stretch of the imagination to believe that the man was actually kidnapped as part of a conspiracy of other labor unions.
Jimmy Hoffa's 1975 kidnapping/disappearance was not caused by rival labor unions. There are still rumors about his death that will probably never be answered. It is easy to say that he was not liked by a lot of groups that he was tied to and I think to narrow that down to one would be a mistake.
It's hard to say whether rival labor unions are responsible for the 1975 kidnapping of Jimmy Hoffa. In reality, a number of things could have happened to him unrelated to the labor unions. There's no way to tell what actually happened at this point, but labor unions likely weren't involved.