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.
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.