I have been working for my company for 9 yrs and recently applied for a different position. Now they are possibly saying that I make too much money to go to this said dept. Is this something they can do to me if I have the hr wage I have due to experience and tenure? I may also add the starting pay for the dept I would be applying for starts out more money hourly than my current job when I started. ( also pay scale for starting pay for my dept has not changed in 9 yrs)
Yes, any different position is evaluated separately at the discretion of the company unless there is a policy expressly against it. You're not getting a pay cut in situ. Having said that, it's an application, you can negotiate or decline to apply.
More than likely they want to discourage you a bit because it's cheaper for them to get someone new and your experience may not be directly relevant to the position (or not relevant enough to make a difference).
To my interpretation, your title and body of your question don't match.
Can a company Reduce employee's pay due to changing the departments within the same company?
makes it sound like you've already moved departments, and they're now trying to reduce your pay.
I [...] recently applied for a different position. Now they are possibly saying that I make too much money to go to this said dept.
makes it sound like you haven't moved yet. In fact, it sounds like they're saying "we're not going to let you move departments, because you cost too much".
So which is it? Assuming it's the second one, well what is there to do? They don't want you to move departments because you're too expensive for the second department. So the simple solution is not to move departments.
If you're desperate to move departments then you need to start negotiating somehow, and possibly end up taking a pay cut. But it's not being forced on you, as far as I can tell, you'd be choosing to take a pay cut in order to move departments. In which case it'd be legal in all countries that I know of (which is only UK and (vaguely) USA...)
Unless there is some law or rule, they can.
Even though the new position may be more attractive from some points of view, the company may consider that it does not return enough benefit to justify the higher salary.
Possible solutions (not exhaustive list):
Negotiate the terms of the new position: get more responsibilities, get involved in other (compatible) activities as well.
Find another position, which justifies a salary at a level that you can accept.
If the current job is better (overall) than the alternatives of changing, keep current job.
Last resort, you can find job at another company.
While some companies have an internal rule that an employee's salary cannot decrease (unless the employee is guilty for something), this is not established in all companies.
Is this something they can do to me if I have the hr wage I have due to experience and tenure?
Yes that is exactly something that they can do.
You might be overqualified for the position. If they are expecting people with 3 to 5 years experience to be selected for the position and you have almost 10 years experience, you may be hitting the top of the salary scale for the position. Or in your situation you are exceeding the scale.
Their options are to select somebody that is below the bottom of the scale and give them a raise; or who fits into the scale and give them little to no pay increase; or select somebody above the pay range. If they pick somebody that exceeds the top of the scale they either overpay the employee or cut their pay. Sometimes when they are desperate they will overpay, but not when they have many qualified candidates in the first two groups.
Even if you accept the pay cut, it might be even more painful. You may find that they will only give you a pay increase when the bump up the pay scale for the job description. That might not happen every year. It could be a while before you see any raise at all.
They also realize that an employee that accepts a large pay cut may also be desperate, which means they might be accepting the drop in pay because they may be leaving soon anyway. Or the employee might think the better conditions are worth the pay cut but will leave in a year or two when they want more money.