Besides the compelled service? Do I really need more than that? If the UBI goes to everybody, which is has to, the U in UBI, I have no way to reject that money, and thus the work. So it's going to cost me a weekend and pay less than minimum wage AND I can't pass on this opportunity? No principal objection to be found there, right?
If there is actual work to be done, then the government should hire competent people to complete the task. Compelling people to do it, part time, will lead to the worst kind of waste. Sloppy, half-assed projects. A contractor, who hires staff to half ass it risks losing those contracts. There really is no penalty for someone to half ass it.