I don't make any money from you reading this, but I commend you looking into the details of this story so a special post on the topic. Sorry people paid to tell you the news couldn't bother to explain this stuff. Here are the Wisconsin Senate Rules. You won't find what you're looking for though, because the quorum rule that allows the State Senate Democrats to stop the Senate from conducting business is actually found in the Wisconsin State Constitution, Section 8, Article 8, which says:
Article VIII, §8If you don't know what "quroum" is, it simply refers to the minimum number of members of a body that need to be present in order to conduct business as that body in the official sense. So, 1 US Senator cannot claim to be "the Senate" and speak for the entire body, or pass a bill for them. Neither can 2. But say 70 Senators get together somewhere, should they be allowed to conduct formal business of the Senate? That's what quorum tries to address. For fiscal bills like the one under dispute, Wisconsin's constitution requires that 3/5th of the members of each chamber of the legislator be present to hold a vote on the bill. This applies even to things like Condo boards and Rotary club executive meetings. Usually most bodies have settled on a majority of members to constitute a quorum.
Vote on fiscal bills; quorum. Section 8. On the passage in either house of the legislature of any law which imposes, continues or renews a tax, or creates a debt or charge, or makes, continues or renews an appropriation of public or trust money, or releases, discharges or commutes a claim or demand of the state, the question shall be taken by yeas and nays, which shall be duly entered on the journal; and three-fifths of all the members elected to such house shall in all such cases be required to constitute a quorum therein.
I don't know why Wisconsin chose to have this requirement in its Constitution. However in my experience, usually supermajority requirements for "fiscal" matters (especially tax increases) are put there by conservatives to prevent anyone from raising taxes. Notice that the article for Wisconsin does not require 3/5th attendance to lower taxes. Lowering taxes can create a deficit. If raising taxes is such a weighty matter to require supermajority attendance, why can they be lowered by a simple majority? So it appears to be a bit ironic that this article is blocking conservative legislators and the conservative governor from taking away powers from unions.
What the Wisconsin Senate Democrats are doing is not new in the annals of legislative history. For example, the US House of Representatives used to have a thing called "disappearing quorum" where members would simply not respond to quorum calls so that the House would have to halt official business if something they didn't like was about to come up for a vote and might actually pass. This practice ended with Speaker Reed in the 1890s, which was the last vestige of non-majority rule of the US House. The minority's ability to stymie the majority has continued in the US Senate to this day, with the vast majority of filibusters conducted by conservatives (usually Republicans but sometimes conservative Democrats).
You might be inclined to disagree with the fact that the minority party can stop a bill just by not being in the chamber. If so I hope you were also upset at the US Senate Republicans over the previous 4 years, who, with as few as 40 members were able to stop an a historically unheard of number of things from passing by use of a slightly different means of minority obstruction, the filibuster (but the effect is mostly the same).