A new attendance policy is going into effect 10.1.17 that is more restrictive than the current one. The timekeeper mentioned he is going back one year from 10.1.17 to enter all previous unscheduled absences. The new policy will be administered for any/all occurrences from 10.1.16 to current. Is this legal? I work for a very large company and find it odd that they can do this.

Why is it odd? Why would it be illegal? Going back a year will let them see who the worst offenders are. Now if they are going back a year and will punish or fire people for a policy that wasn't in place when the events took place... then you have grounds for a grievance.

As it is, I see this as a way to determine who needs extra scrutiny as some people WILL abuse the system. And since it's a very large company it would allow them to streamline that. Only a small percentage of the company would be doing that. They have always been watching... apparently they saw reason to make changes that will take effect NOW for the rest of the year, and since leave is usually based on the calendar year, the people who abused it earlier this year won't get a chance to continue the next few months.

Unless you were one of the people stretching policy to the breaking point and then some. You have nothing to worry about.

I've worked a lot of places the last 40 years. And every office will have someone who will milk it for all they can get away with. And it always makes it hard on the rest of the people when they have a legitimate need.

You don't even say what the new policy IS. You don't say what happened when there was a unscheduled absence.
What could that possibly mean, besides sick days? Personal days? Whatever you felt like not showing up for? Were you paid, or not? Did it get taken from vacation time?
We can't possibly tell you what is legal.

I would consider myself lucky.
Many companies put more restrictive policies in place during the recession of '08.