How to block a user from starting a transaction

We have a service account that is running queries to pull some data.  It has read only access to the tables, but, unfortunately, the tool is starting a transaction before it reads the database.  The query takes more than 20 minutes (21 - 23 minutes), so we're getting the console message that the transaction is open longer than 20 mins.  Is there a way to prevent a user/service account from being able to start a transaction since it only has read access to all of the tables in the database?