You will get a notice of overpayment if the SSA thinks they paid you more money than you should have received. If this happens, you can:
1) File for reconsideration if you think the amount of the overpayment is wrong or there was no overpayment.
2) File for a waiver of repayment if you think the overpayment was not your fault and you cannot repay the money. A request for a waiver asks SSA to free you from having to pay back the overpayment.
If you do not want your checks reduced while you are contesting the overpayment, SSA should stop trying to collect the overpayment if you:
a) Ask for reconsideration or waiver within 30 days of the date of the overpayment notice, or
b) Ask for waiver at a later time. (If your request is more than 30 days after the date of the overpayment notice, SSA probably will have started to try to collect the overpayment. But they should stop when you make your request.)
If the overpayment is not successfully contested, and SSA does not waive the overpayment, and you are continuing to receive benefits SSA will recover the overpayment from the money you are being paid. If you are not receiving benefits it is very unlikely that SSA will take action against you to collect the moneys. Normally SSA will simply wait until you are again entitled to benefits and recover the overpayment at that time, without interest.