Can an End Buyer put a lien for "Executed Labor"?

[Rhys Royales]

I have assigned a contract in Maryland to an end buyer for a property owned by a foreign family that needs to get an ITIN and FIRPTA from the IRS. I have expressed upfront to the end buyer that the closing process could take months since application for ITIN and FIRPTA could take weeks. There was a delay on the seller's end to start the application of the ITIN and FIRPTA because the end buyer wanted to renegotiate the price of the property. On top of that, the previous government shutdown delayed the process as well. As we come nearer to the closing deadline, I requested a contract deadline extension from the seller which they willingly agreed/approved. Upon letting the end buyer know that the closing deadline has been extended in case the ITIN and FIRPTA won't get on time, the end buyer threatened that they have been patient long enough and will require either:

1) addendum to include an allowance for an extension of a per diem charge of $100 past the agreed upon 12 week date.

or if I do not agree with this,

2) they intend to place a lien for the "executed labor" that has already been completed.

Key notes are: 1) No one allowed the end buyer to do any work on the property and; 2) I just checked the property this week and there are no significant changes or improvements on it.