No system of taxation currently in use distributes the financial burden in a completely fair way. I think this is something that just about everyone will agree on, though where exactly the unfairness is located is a controversial question. I do not mean that the unfairness is intentional or even foreseen by the legislators, but more like this: there will either be a pair of individuals A and B such that it would be fairer if A were taxed more and B less (it's also possible, but less likely, that (a) everybody is taxed more than justice allows or that (b) everybody is taxed less than justice requires; I'll neglect (b), and leave the extension of the arguments to (a) as an exercise).
This is not something we can complain about much. No legal system can cover all cases adequately. But here is an interesting consequence: An across-the-board increase in taxes is very likely to exacerbate some instances of injustice. For if fairness requires that A be taxed more and B less, then when we raise A's and B's taxes, we will likely be overtaxing B by a greater amount than before, and hence the injustice to B will very likely be the greater. (This can be controversial. One might think that what matters are the ratios, not the absolute amounts. I am inclined to disagree.) This means that we have a prima facie consideration of justice against across-the-board tax increases.
Moreover, I think the above considerations generate a prima facie consideration of justice against government spending. For if overall spending were even slightly lowered, a slight across-the-board decrease in taxes would be made possible, and that would slightly decrease the severity of the unfairness to B.
Of course, the reasons above are only prima facie and defeasible. Double Effect can permit the increase of spending and across-the-board increase in taxations when the injustices are not intended and a sufficiently serious good—perhaps itself a good of justice—is being pursued. So while the above considerations sound like they would generate fiscally conservative conclusions, in practice the effect of the considerations could be quite small or nonexistent. Or it could be large. I don't know. But it is still interesting to me that the defeasible reasons against spending and across-the-board tax increases are reasons of justice—I didn't think of them that way before I noticed the above arguments. And I suppose it would be healthy for legislators to think of them as reasons of justice, if they are indeed such.
A weakness, however, in the above arguments is that it is not clear whether it makes sense to talk of unintentional injustice. If I am convicted of a crime I did not commit, but on excellent evidence and with solid legal procedures, have I really suffered an injustice? If the answer is negative, then we may not be able to say, strictly speaking, that B has suffered an injustice by being taxed too much. Maybe, though, the thing to say is this. My conviction of a crime I did not commit is not an injustice; but justice requires that such convictions be minimized. Likewise, the allocation of too high a tax burden to B is not an injustice; but justice requires that such misallocations be minimized.
The incorrect conviction analogy also suggests that we have a prima facie reason of justice not to increases criminal sentences across the board. For each across the board increase of sentences is likely to result in some innocent serving an even greater sentence than otherwise. (However, there is a difference with the taxation case. For while justice does not intrinsically call for taxation (though taxation may be a necessary means to ends that justice requires the pursuit of), justice does intrinsically call for the punishment of the guilty.)