A basic income that truly covers the basic needs of modern life (food, shelter, electricity, running water, heat, healthcare, broadband, education, etc.) would give the lowest paid workers bargaining power.

A basic income that doesn't cover those things might instead just make it easier to pay workers even less.

Think of what some restaurants do when their employees get tips: they pay less than the legal minimum wage because they expect tips to "top off" worker earnings until they meet minimum wage requirements, so they explicitly pass that tip from customers into the business's revenue stream, skipping the intended tip recipient altogether. If we don't protect recipients of UBI, their employers can do the same thing.

Because of active union-busting efforts, which have made it hard for these workers to organize collective action.

Walmart: https://www.theatlantic.com/business/archive/2015/06/how-wal...

Whole Foods (post-acquisition): https://www.theguardian.com/business/2018/sep/27/amazon-whol...

Uber: https://www.theguardian.com/us-news/2019/mar/22/uber-lyft-ip...

Amazon: https://gizmodo.com/amazons-aggressive-anti-union-tactics-re...

This is not a new problem; low-wage workers have always had the collective power to force change, and businesses and business-friendly have always worked tirelessly to disrupt that collective action.

How many of those employees have alternate work they can take if fired or have enough money saved up to make ends meet if they don't get a paycheck for a while? Many people live paycheck to paycheck and theres a huge batch of people newly unemployed to compete with for jobs. I don't think that's a lot of power. Without a union, theres also challenges in organizing such an event.