Do you work part-time and get Working Tax Credit or Housing Benefit?
Did you know that once you're on Universal Credit, you'll be expected to attend the Job Centre to prove that you're looking for better paid work / more hours, in much the same way as unemployed people must prove they're looking for work.
If the Job Centre find an interview for you, you will have to attend (with 48 hours notice) even if it clashes with your paid work.
If you are offered a job with more hours, or better pay than your current one, you will be obliged to take it, even if you have good reason for not wanting to e.g. it's only a temporary post (whereas your current one is permanent) / has no training & worse prospects than your current job / makes picking your children up from school impossible / requires you to travel much further / has nothing to do with the career you're following.
If you don't attend the interview and/or take the job, your UC will be sanctioned, you will lose the UC for months or even years (depending on if it's your first infraction).
You will be forced to continue "upgrading" your job until you earn the equivalent of minimum wage for 35 hours a week.
I suspect there are lots of people (e.g. parents who work part time so they can pick their kids up from school) who will be affected by this, but don't realise it yet.
More info here