Stop Unfair Bid Shopping Act of 2019 or the SUBS Act This bill requires prime contractors under federal construction contracts to notify the government of changes in certain subcontractors performing contract work. Specifically, the bill requires an executive agency awarding a construction contract using sealed bid procedures in an amount greater than $1.5 million to, among other things (1) require an offeror for the contract to include a list in the offer that includes each subcontractor that the offeror intends to use, for any subcontract expected to be awarded in excess of $100,000; and (2) include a clause in the contract requiring that the prime contractor submit to the agency a written notification of any subcontractor substituted after the award of the contract for a subcontractor listed, along with an updated estimate for the cost of performing the work associated with the substituted subcontractor. If the prime contractor notifies the agency of a substituted subcontractor and the cost of performing the work associated with the substituted contractor is estimated to cost 10% or more than the cost for performing such work as bid, the contracting officer for the contact may modify the contract to reduce the amount of the contract award to take into account the substitution of the subcontractor. The bill excludes from its scope contracts for the Department of Defense or any military department but includes the U.S. Army Corps of Engineers.