(CNN) All but three of Detroit's 97 schools stayed closed again Tuesday, the second day of teacher protests over pay concerns in the city's financially ailing school district.

On Monday, the same number of schools closed after more than 1,500 teachers called in sick to protest when they learned the district has only enough money to pay them through June 30.

Because some teachers can elect to receive their paychecks year-round, the union representing teachers argues that shortfall means those educators have already started to work for free.

"Detroit Federation of Teachers leaders spent the day meeting with DPS Transition Manager Judge Steven Rhodes and other decision makers to get an assurance that our members will be paid for their work," the union said Tuesday. "Still, they refuse to say the three words our members need to hear: 'I guarantee it.' "

"Their failure to give us that guarantee is tantamount to a lockout." the union said.

More protests are planned for Tuesday as parents caught in the middle of the debate scramble to arrange for child care.

American Federation of Teachers President Randi Weingarten said Tuesday on Twitter that she is headed to Detroit to join the demonstrations.

Ironically, all of this turmoil is happening during National Teacher Appreciation Week -- an observance the Detroit Public Schools system is touting on its website's homepage.

By the numbers: Detroit teachers' 'sickout'

94: The number of public schools closed

97: The total number of schools in the system

1,500-plus: The number of teachers who called in sick in protest

3,000: The estimated number of public school teachers

63,716: The average salary, in dollars, district teachers earn

Why is this happening?

The Detroit school system is deep in the red, with more than $500 million of operating debt, the Michigan governor's office has said.

Teachers union interim President Ivy Bailey told educators Saturday that the school system only has enough money to pay its teachers through June 30. And that means some may not get paid for their work as the school year winds down, the union argues.

"There's a basic agreement in America: When you put in a day's work, you'll receive a day's pay. DPS (Detroit Public Schools) is breaking that deal," Bailey said.

The average teacher salary in the district is $63,716.

Union officials believe about two-thirds of Detroit teachers opt to receive paychecks throughout the year, not just during the school year, according to Richard Fowler, a spokesman for the American Federation of Teachers -- the parent organization of the Detroit teachers union.

School officials have not corroborated those numbers.

The union planned to run a newspaper advertisement Tuesday pitching its case.

"It's the law that when you work, you get paid," the ad says. "Asking teachers to work without pay is un-American."

Teacher salaries are the latest casualty of the financial crisis in the district. With so much money going to pay down debt, many of the school system's facilities have fallen into disrepair, teachers say.

Teacher strikes are illegal in Michigan. So to protest the poor conditions that educators say they and students must deal with, Detroit Public Schools teachers have relied on the so-called sickout method -- calling in sick en masse, forcing schools to close.

In January, teachers staged a sickout to protest dilapidated and dangerously unsanitary conditions -- including rat and roach infestations, black mold and falling ceiling panels -- forcing the closure of dozens of schools. A judge later ruled that teachers could continue staging the sickouts after the district brought the union to court over the issue.

That's why they are using sickouts to protest the news about pay.

Hundreds of people attended a rally in support of the teachers Monday outside a school district administration building, according to Nikhol Atkins, a staff member at the teachers union.

"I support the teachers on getting a fair deal. They're educators," said parent Tony Kinsey, whose sons are in the 11th and ninth grades. "I'm frustrated with the adults, the leadership. Our children are the ones suffering."

Teachers and some parents are urging Michigan lawmakers to pass a $715 million education reform package that would fund salaries for July and beyond.

The legislation has passed the Michigan Senate but still needs to be approved by the House of Representatives and Gov. Rick Snyder.

"I have been and remain confident that the Michigan Legislature understands the urgency and importance of the reform legislation that is before it," said Judge Steven Rhodes, whom Snyder appointed in February to be the transition manager for Detroit Public Schools. "The future of Detroit is as much at stake here as the future of the school system."

Rhodes called the sickouts "drastic" and "unnecessary" but said he was sympathetic to the teachers' plight.

"I am on record as saying that I cannot in good conscience ask anyone to work without pay," he said. "Wages that are owed to teachers should be paid. ... I understand the frustration and anger that our teachers feel."

If not school, where do kids go?

Sharlonda Buckman, CEO of Detroit Parents Network, an organization of parents with children in all city schools, said she felt an "instant splitting headache" when she heard about the sickout.

"This is one of the most tumultuous school years our kids have experienced," she told CNN. "They aren't getting what they need. It's disturbing. First in January ... (now) we're in May and this is still happening."

Buckman has nieces and nephews in the public school system. She points out that not every parent has the flexibility to stay home from work or to be late when faced with closed schools. Older children have to baby-sit younger ones, and some kids are left entirely alone.

"This creates a safety issue when you have unsupervised children," she said.

It's also a challenge for parents such as Kinsey, who works from home but has had to interrupt work three or four times to cajole his sons to do schoolwork. His 11th-grader needs to prepare for the SAT, he said.

"I gave them a couple choices as long as it was learning," said Kinsey, who made reading assignments for his sons. "They think this is a vacation. My oldest wants to go to the movies and the mall. It's been a lot of negotiating, going back and forth and empathizing with them. It's been tough."