From the SRH:

"Do I have to accept the trip?
A pilot is considered to have accepted a pro er if he has verbally accepted the assignment from a schedul- er or acknowledged the rotation via IVR, the Crew Auto Noti cation System, or iCrew. When speaking to a scheduler, a pilot should ascertain whether or not the award or assignment is a pro er and, if unsure, should simply ask the scheduler.A pilot’s obligation to accept a trip on X days or regular line o days is not absolute, regardless of whether the trip is or is not a pro er. A variety of circumstances might prevent a pilot from accepting a trip.
For example:
• Not being physically located so as to be able to report.
• Having recently consumed alcohol.
• Lack of available child care.
• Lack of available transportation.
• Not being adequately rested. For example:
A pilot, not on call, noti ed of a rotation with a report time within 10 hours should consider if he
is su ciently rested to accept the scheduled rotation.
A pilot is not required to accept an inverse assignment that does not allow for 10 hours of rest
between acknowledgement and report time for the assigned rotation."

Bottom line: Never answer a call from Scheduling unless you're on short-call. This technique avoids this can of worms to begin with.