Why?
"...an industry that needs a union.."
Why?
"...more union-friendly in the coming years"
Why?
Nothing you said is grounded in any actual analysis or verifiable facts.
I'd argue that undifferentiated skills that require little education make this an industry poorly suited to unions; Even if you unionize you have little chance of success since most workers are easily replaced by scabs or increased automation. Many workers are also kids in school (speaking from experience -- I used to work in a produce department while studying),and so would not join a union regardless due to the temporary nature of their employment. Butchers and bakers may be an exception, but these are the minority compared to checkout workers, stock boys, or produce workers.
So maybe they'd benefit significantly from the fruits of unionization as experienced in more technically complex industries...but they are highly unlikely to receive those fruits.