On Monday, Wisconsin became the 25th so-called “right to work” state when Gov. Scott Walker signed a bill into law that undermines workers’ rights and is likely to reduce wages in the state.

This divisive bill, which would have more accurately been called a “right to work for less” bill, was fast-tracked by Republican leaders despite being met with intense resistance and had the support of major right-wing funders. Two outside groups in favor of “right to work” legislation, Wisconsin Manufacturers & Commerce and the Koch-backed Americans for Prosperity, spent over $5.5 million in support of Scott Walker’s reelection bid. Analysis by the Wisconsin Democracy Campaign found that since 2013, Republican legislators in the state have accepted “$26 in contributions from business interests for every $1 in labor contributions.” And the right-wing Bradley Foundation has given millions to groups promoting “right to work” bills, including to a number of groups in Wisconsin.

In Wisconsin and across the country, when people can “follow the money” and see who is bankrolling elected officials and what their agenda is, it changes how they evaluate the bills being considered. But today it’s not always possible to follow the money. Major corporations can funnel an unlimited amount of money through “dark money” groups to influence the political process, and they can do so secretly.

President Obama can, and should, take a big step to shine a light on dark money by issuing an executive order requiring companies that contract with the federal government, companies like Verizon and Lockheed Martin and Exxon Mobil, to disclose their political spending. No matter the issue, voters deserve to know who is trying to buy influence in their state or national government.