The waiters at Johnny's restaurant, Dan and Sam, have been asking Johnny for weeks about getting an increase in their hourly rate. Johnny repeatedly explained to Dan and Sam that he cannot agree to a pay rise without first speaking to his accountant, and that he will not have time to do so until the end of the month. Dan and Sam are becoming increasingly frustrated with Johnny's refusal to consider their request. One Friday evening, during the busiest part of the shift, Dan and Sam confront Johnny and tell him that unless he agrees to increase their hourly rate by $5 per hour, they are going to walk out, leaving him to serve the customers on his own. Johnny feels as though he has no choice but to agree to their request. He promises to adjust their pay as requested.

Is Johnny legally obliged to keep his promise? Explain your answer.