Will getting legal custody stop my ex from moving out of state?

I have 3 kids with my ex-husband and since our divorce, my kids have lived mostly with him because he lives closer to their school and friends. I had to move farther away to find a house I could afford after the divorce. I do get alot of time with the kids under our divorce agreement. Now their dad is saying he is moving from Indianapolis to Chicago, over 3 hours away. If he does that and takes our kids, I won’t be able to see them at all during the week or go to any of their sports or activities. Even weekend visits will mean over 6 hours round trip in the car for them. I don’t necessarily want to change physical custody if the kids stay here in Indianapolis because they are happy and doing well. But I don’t want them moving 3 hours away. Can I ask a court for sole legal custody to stop their dad from moving with them? Is the fact that his move would make our custody schedule impossible under the current settlement agreement matter? Can I enforce it and stop the move?