I may well stand corrected. Based on a joint assessment I'm assuming that the OP is referring to a salary base that maximises the lower tax rate. This would not be a significant salary & anything paid above that limit would afaik not reduce the overall tax payable. Out of curiousity why would the Revenue have an issue here?
Precisely because an artificially high salary has the effect of maximising the lower rate band, and thereby reducing the income tax liability. Artificially being the operative word.
Take the case of a small Ltd co. generating enough cash that the proprietor can afford to pay himself a salary of 60k Gross - assume for the purpose of this illustration that his spouse doesn't have a separate PAYE employment using up any of her std rate band.
On a salary of 60k gross, with all of it being paid to one spouse the net pay comes out at about 41,500.
If they decide to pay the husband 40k gross and the wife 20k gross, the net pay is about 46,100 (assuming the wife goes on Class S PRSI, which I'm not going to get into here).
So that's tax of 18,500 under the first scenario or 13,900 under the second scenario, a difference of 25%. Therefore, Revenue may well want to know that a spouse, with a salary that conveniently uses up the standard rate band, is in fact active in the business and being paid an amount commensurate with the work performed...