Voter Fraud was the argument for the original poll tax laws in the South

Opinion piece in Politico provides the historical context:

Southern states in the 1890s enacted literacy tests, poll taxes and other laws to regulate voting. Politicians who wrote these laws made no secret of their belief in white supremacy. And most Southerners understood that these laws were designed to keep African-Americans and other targeted groups from voting.

But there was a problem: the 15th Amendment to the Constitution. Adopted in 1870, the amendment prohibits any state from depriving citizens of their right to vote based on race. This meant that the poll tax laws could say nothing about race, and the Southern political leaders could not write their real intent into the law. They needed a pretext.

What they came up with was voter fraud. There was plenty of irony in this — because these same politicians who supported the poll tax had raised election-rigging to a high art. Many had been involved in vote-buying schemes, and fixing elections by “counting out” the other side.

The poll tax would do little to prevent such fraudulent voting tactics. But, just as its supporters intended, it put another barrier between minority and poor voters and the ballot box.