(CHICAGO) Schools chief Forrest Claypool has encouraged teachers to show up at schools on Friday, the day their union called for a strike, saying they’ll get paid.

But that money may not stay in their pockets for long, the Chicago Sun-Times is reporting.

Teachers who do report to schools for work inside rather than for picketing outside “shall be fined the pay earned on the days worked during the strike,” according to written CTU strike policy. “Fines shall be payable to the Chicago Teachers Union.”

CTU Vice President Jesse Sharkey said the union isn’t threatening anyone as it gears up to draw attention to a lack of state funding for schools throughout Illinois.

“Now isn’t the time for us to start planning what actions we’ll take against our co-workers,” he said.

“The most important thing is that April 1 is an official strike action,” sanctioned by 80 percent of a vote by the union’s governing body, Sharkey continued. “If someone chooses to work anyway, crossing the picket line is a serious offense in union principles in which they put their personal consideration over their co-workers.”

He added that the CTU has no power to take anyone’s money but requires the fines to reinstate membership.

The union raised the issue in a letter to whom it considered strikebreakers during the 2012 strike, but a union spokeswoman couldn’t immediately say Monday if the union had collected any fines from people who crossed the line.

“Your compliance with the union strike policy will do much to restore unity and goodwill at your local school,” read a letter obtained by the Chicago Sun-Times from financial secretary Kristine Mayle to one accused strikebreaker in early 2013.

Those who balk at paying can be tried according to a process laid out in the CTU’s constitution, and then suspended or expelled from the union.

The union’s “Day of Action” will begin outside schools at 6:30 a.m. Friday with picketing, and will include staging a mock funeral at 10 a.m. at Northeastern Illinois University, 5500 N. St. Louis, illustrating the death of higher education in a state still stuck without a budget, and end at 4 p.m. outside the Thompson Center, 100 W. Randolph. En route to the Thompson Center, teachers will stop at 2 p.m. outside City Hall to demonstrate, officials announced Monday.

Contingency plans for the more than 300,000 affected CPS students are coming Tuesday.

In 2012, when CTU members walked off the job for a seven-day contract strike, 19 people were determined to be strike breakers, according to CTU spokeswoman Stephanie Gadlin. She wasn’t sure how many have since been reinstated.

CPS spokeswoman Emily Bittner said 100 CTU members were reported as going to work then. The district refused a union request for all their names, she said.

Anyone suspended or kicked out of the CTU can still keep their CPS job, according to the district. Those people lose their voting power as union members but still have to pay dues, the union said.

The House of Delegates voted 486-124 to strike on April 1. Yet in a union that typically acts in lockstep with its leadership, several teachers have told the Sun-Times they were loathe to miss another day of school a week after the district’s first of three unpaid furlough days because they didn’t want to lose a teaching day for their students or their money.

The teachers’ contract expired June 30. The district and union continue to bargain.