For one thing, it allows large corporations to increase their influence, by helping people that are vested in protecting their interests vote for candidates who support those companies. If a large enough set of employees is in one area, that could swing a local election. Two, a lot of these employers would appear to employ people along a particular side of the political spectrum.

Combine these aspects with the fact that it would probably be easier for these large companies to switch a current day off to election day, rather than small companies who may not be able to afford it, if they give days off at all. It could end up having decidedly biased impacts on what political party is in power, and what industries get more power.