Anyone with such an employer would hopefully quit, now that they have the security of the guaranteed minimal income. Which means that this is to some extent a worker protection scheme: Employers will have to make menial, badly paid jobs more attractive since they will now be competing against "no work for the same money". In theory, at least. In practice things might devolve into more unreported employment, so workers could get both the full state minimum income and an unreported income on top of it.
This is one of the crucial differences to a proper universal basic income: The UBI does not discourage taking a job that adds income to the UBI. This kind of minimal income scheme does discourage taking badly paid jobs, since the total money you receive remains the same whether you work or not.