They're likely to be told to belt up? (4-4,7)

'they're likely to be told' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'belt up?' is the wordplay.
I cannot quite understand how this works, but
'belt' could be 'seat' (seat belt is a kind of belt) and 'seat' is found in the answer.
This explanation may well be incorrect...

'to' is the link.