Use of data by third parties

I have performed some field work (specifically an as built survey on the sanitary sewer and storm drain systems of a new subdivision) which the general contractor in charge of building the subdivision has not paid for. The data from this field work has been forwarded to a local engineering firm in order that they can satisfy city/county requirements for as built data. My question: What is the general opinion concerning contacting the local engineering firm and issuing a statement regarding the use of this intellectual property without payment? Should the engineering firm honor such data as still being the property of the surveyor until such time as payment is made by the contractor before utilizing said data? Would contacting the engineering firm be ethical?

Do you think you won't get paid? If so, you should not release the information without payment.

It is not ethical for the engineering firm to use your data if you have not been paid. It is in perfect order to make the engineering firm aware or ask if the client has made them aware you have not been paid for your work.

What does your contract say?
MLB

I would talk to the engineering firm.  They may be the next in line to not get paid and would probably like to know your situation before they hand over deliverables over as well.