Does initial snapshot process lock tables when setting up transactional replication?

When you configure SQL 2012 Transaction Replication, does SQL Server place any locks on
the tables (the ones you have selected to publish) when it generates the initial snapshot files?
I have some tables (articles) that have 2M+ rows and I don't want this snapshot process
to cause any performance issues in production.  If the tables are being locked for 
the duration of the initial snapshot process, then I want to do this off peak hours.  

Can someone clairfy this?

Thanks!