Today, unions are puny. They cover around 10% of the workforce.
At it's peak, the labor movement covered around 35% of the workforce, and the majority of families had at least one member, who could get insurance coverage for the household.
One of the reasons for the decline is "secret ballots".
Until 1947, people could sign up with a union by writing their name on a card, declaring their wishes. If the majority were willing to sign, then the union was in.
Business didn't like this, so they demanded a secret vote procedure, and introduced delays into the system. That way, during the time between a request for an election and the election itself, the company could intimidate its workers.
Shortly after the ballots were introduced, union representation has declined to its current, sad state.
Back in the 30s, during the Depression, millions of Americans joined "the union" by signing a card. They didn't even sign it at their workplace -- they joined the unions directly, as members, then caused their workplaces to become unionized. (That is the total opposite of today.)
Needless to say, the business interests fighitng Employee Free Choice don't want to see a replay of the 1930s. They don't want to see the suffering people gain the rights that would lead to their self-improvment and economic empowerment during the subsequent economic boom.