If you have an Offer in Compromise (OIC) under investigation (being reviewed or pending) by the IRS, they may still be able to file a Notice of Federal Tax Lien claim against you. The applicable Statue of Limitations regarding your federal tax lien is extended, in other words.
The pending period involving your OIC starts when an IRS employee determines that your IRS Form 656 is ready for processing.
The pending period will continue until there is a final determination by the IRS
as to whether it rejects, accepts, or acknowledges withdrawal of the offer in writing.
If you find out that your Offer in Compromise has not been accepted by the IRS, you may appeal the decision. At this point, your Offer in Compromise will be treated as pending.
The pending status is only removed when a final decision has been made by the IRS.