Why does Hugh stop allowing Douglass to hire out his time? How does Douglass react?

Normally Douglass returns the money he has earned to Mr. Auld on Saturday.  In August, however, he is delayed by a meeting in town and is not able to return until the next morning.  Mr. Auld becomes angry and says that from now on Douglass must work for Auld on Saturdays.  At first Douglass refuses to work on Saturday which then creates a standoff between the two men.