I asked the same question of another operator. They said YES!
I told them to take a hike. I mean No Thanks.
The truth is I don't think so. I have been in this industry for my entire life. I have had a father and his father in the business. I have never heard of anyone doing it.
I don't sign contracts. I have my reasons. Many have been echoed here plenty on the forums.
I always think the operator is a scumbag when I hear or see one. And, that is for an initial and NOT a re-current.
So, the long answer is NO I don't think they are common.
Of course I am leaving aviation since it has lost its collective mind and sense of direction. We keep producing young and inexperienced pilots that are willing to fly at any cost. And, then they wonder down the road why they can't get a pay check that is commensurate with their job.
This cycle is going on while in the midst of a good economy. I can't fathom what the owners/operators will come up with after the economy takes a down turn.
The problem is that there are way to many young inexperienced pilots willing to continue to build time and move up that you are forced to sign and take the wages offered or move on.
Oh, never forget...."Never under-estimate a pilots ability to take a bad job."
This keeps the owners/operators happy knowing that if you don't they can find a (deep in debt) sucker next in line.
Peace and Good Luck.
Edit: Spelling errors.