How does a decrease in the money supply affect taxation?

First you must explain what you mean by decrease in money supply? Do you mean for example the US not having enough cash? Or a persons wage being decrease. I would assume you are asking about the second one as the US can just make more dollars bills. As to answering the question taxes depends on you income. Therefore if you make more you pay more, make less you pay less. The government running out of bill or you making less money won’t affect taxation in general but only you personally as the government is flexible to meet your needs.