Public opinion on unions in the US has always been mixed, going up and down.
The Cold War led to rhetoric falesly accusing anyone who cared about the lower classes to be Commies. Chomsky has pointed out that, in a democracy, propaganda is a key element the powerful use to keep the powerless in line. Propaganda does work, but only when the economy is doing well. People are less willing to accept lies when they are personally suffering because of those lies. That is the situation that has been developing lately, and so unsurprisingly union support is growing again.
The young are more supportive of unions (and more liberal in general) than older generations (even when those older generations were young themselves). This new liberal young generation is also the largest generation in the US. It would be counterintuitive for the support of unions to not consistently rise in the coming years and decades.
Just to give some context, consider public opinion of unions over the past 80 years:
Notice how in the entire history of polling that approval rating has never been below 50% and the disapproval rating has never been above 50%. For most of US history, the approval rating has been massively high. It was only with recent hyper-partisan politics that there has been a small drop that is now once againg rising.
Also, consider public employee unions. They are the easiest targets to attack. If support for unions was down, support for public unions would be in the gutter. However, that isn’t the case:
If you want a fair presentation of public opinion, the following are some good sources of recent data and analysis: