Kentucky's largest school system will be forced to shut down Thursday after thousands of teachers called in sick as part of a statewide "sickout."

Jefferson County Public Schools said late Wednesday night that it does not have enough substitutes to cover the number of absences reported.

Fayette County Public Schools, the state's second largest district, also announced it would close due to teacher absences.

The closures come just hours after a grassroots group urged teachers to call out sick so that they could travel to Frankfort in protest of a bill that would restructure the board that oversees the state's teacher pension system.

The list:These Kentucky school districts are closed due to teacher 'sickout'

More:Teachers group calls for statewide 'sickout' as JCPS, other districts close

KY 120 United, a network of teachers and other public school employees, issued the call via social media early Wednesday evening.

"Please call in sick tomorrow and text your co-workers to do the same," the group wrote on Facebook.

The group said it is protesting House Bill 525, which would restructure the board for the Kentucky Teachers' Retirement System.

"This bill is as destructive to our pension assets as any bill could be," the post said.

Previously:As Senate budget takes money from teacher pensions to fund others, some claim retaliation

Background:Matt Bevin warns Kentucky teachers against a walkout: 'That would be a mistake'

Mandy McLaren: 502-582-4525; mmclaren@courier-journal.com; Twitter: @mandy_mclaren. Support strong local journalism by subscribing today: courier-journal.com/mandym.