If someone is willing to do this, they are likely to be people who currently are on low incomes and thus unlikely to be paying much tax if any. I think it would have the opposite effect though. In most countries, the welfare system harshly punishes people who do a small amount of work, withdrawing benefit at a very high marginal rate. This is a massive disincentive to finding work. With a basic income, people can for example do voluntary work. People on sickness benefit can gradually try to go back into work, doing a few hours per week. If you can top up your income without being penalised for it I reckon quite a lot of people currently on welfare would start working a little.