Here's the Wisconsin Constitution, Art. IV, Legislature (emphasis added):

SECTION 7. [Organization of legislature; quorum; compulsory attendance.] Each house shall be the judge of the elections, returns and qualifications of its own members; and a majority of each shall constitute a quorum to do business, but a smaller number may adjourn from day to day, and may compel the attendance of absent members in such manner and under such penalties as each house may provide.
and in the US Constitution, Art. I (emphasis added):

SECTION. 5. Each House shall be the Judge of the Elections, Returns and Qualifications of its own Members, and a Majority of each shall constitute a Quorum to do Business; but a smaller Number may adjourn from day to day, and may be authorized to compel the Attendance of absent Members, in such Manner, and under such Penalties as each House may provide.
Those darn black-hatted, Iron Brigaders from Wisconsin were just a bunch of copycats. They did pretty well in the War of Northern Aggression, however.

BTW: Illinois can't fetch Dems, lawyers say:

The Wisconsin legislators on the lam cannot be touched by out-of-state police, according to veteran Wisconsin lawyers.

The attorneys agree that authority of Capitol Police and other local law enforcement ends at Beloit, meaning Illinois officers couldn't help their Wisconsin brethren retrieve those Democrats who escaped if they wanted.
....
Carla Vigue, spokeswoman for the Capitol Police, said the agency has not looked for the legislators nor has it contacted Illinois authorities.

"We're not engaged" in the situation, she said.
....
A similar situation occurred in Texas in 2003 when legislative action there was paralyzed for several days when Democrats ran off to Oklahoma and New Mexico. The Democrats were trying to block a Republican redistricting plan.

The Texas boycotts ended when one Democrat voluntarily returned to Austin. The plan was approved over the objections of Democrats.
So, MSNBC (out of many hyping media outlets) is hyping this aspect of the event.

The noon (today) crowd at the Capitol was very large (jsonline photos; #1).

MJS (jsonline) has the best coverage of this Wisconsin story.

MJS's Politifact column (a regular feature) has 2 pages of links to truths, half-truths and lies re: Statements about State Budget.

For example, this assertion, from Progressive Change Campaign Committee:

Says Wisconsin Gov. Scott Walker "has threatened to call out the National Guard if workers protest against" changes to bargaining laws.
but, from MJS Politfact, after a long discussion of the evidence:

Let’s return to the statement.

The Progressive Change Campaign Committee said Walker "threatened to call out the National Guard if workers protest against these cuts!" The governor spoke of possibly calling up the Guard if state workers didn’t show up for work, but he made no reference to using it in response to protests. And certainly none that would suggest the Guard is authorized to use force to impose anything on state workers.

We rate the claim Pants on Fire.
Finally, Poll: Majority don't side with Walker; senators should come home:

A new poll shows that a small majority of Wisconsin residents disagree with Gov. Scott Walker’s plans to increase public employees’ share of their benfits and to strip the unions of much of their power.

But the poll also says that a stronger majority of respondents think that Democratic state senators, who fled the Capitol on Thursday to avoid taking a vote on the Walker’s legislation, should return to Madison.

The poll was conducted and paid for We Ask America of Springfield, Ill. The poll was conducted on Thursday by sampling 2,397 Wisconsin residents. The margin of error is plus or minus 2 percentage points.

The poll asked respondents if they approve or disapprove of Walker’s plans. According to the poll, 43.05% approved and 51.9% disapproved. 5.05% were uncertain. Females and union households registered higher disapproval.

On whether the Democratic senators should return to Madison, 55.99% said yes, 36.38% said no and 7.63% were not sure. There was virtually no difference of opinion based on gender. ....
My conclusion is that both political parties are trying to manipulate the public via the parties' respective media outlets. I hope both parties fall flat on their fat a$$es (fat because of their fat wallets).

Regards

Mike