We made our employees sign only a 4 lines non compete agreement when they start working 10 years ago. I redid a very professional non compete and confidentiality agreement. All 9 employees signed it, one employee doesn't want to sign it. No good reason given. I cannot even find the original paper he signed (again, only 4 lines).
Can I tell him if you don't sign you cannot work for me anymore or this may have negative legal consequences for me?
Can he argue this is a new request he didn't know when he got employed, or I owe him the money he will lose if i fire him (he is scheduled for few trips). or anything else
Basically is there negative consequences to make a cause and effect: if you don't sign this you cannot work for me anymore?
As previously mentioned, you should hire a labor attorney to ensure that no future issues arise.
I would like to comment that if your employees have been working for you and you are simply asking them to sign a new agreement that includes new terms that benefit you/your company but they are not offering anything new/additional in exchange, then the agreements could be found to be void for lack of consideration (bargained for exchange).
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You cannot make his continued employment conditional on his signing the agreement. What I would suggest is to offer him new consideration (meaning, offer something, such as a benefit, day off, etc, in exchange for his signing). You will also want to make sure that your new agreement is reasonable in both time (number of years it restricts) and scope (location that it restricts). If you don't have his original signature it will be very difficult to enforce, and even if you did, a 4 line agreement is likely not strongly worded enough.