Slickterp
If they ask you to, sure. You can decline, the write up still happens.
STEVEN F
Signing the form only PROVES you saw the form. Refusing to sign doesn't invalidate the write up in any way. At most, refusing would get you in more trouble.
Mr. Smartypants
Employers live in constant fear of being sued. It's expensive for them even if they win. Fairly often they are sued by employees who've been fired, for 'wrongful termination'. New laws are passed every year to protect employers from their employees, so it's almost impossible for an employee to win such a suit these days, but it still happens.
So when they discipline you, or 'warn' you, or chastise you in any written way, they want you to sign it, so they can bring your personnel record to court to show how often you screwed up, and they can't be accused of slipping these warnings into your file retroactively.
They have no power to force you to sign them. But they can also fire you for any reason, or no reason at all.
In my checkered career I got THREE 'written warnings'. A 'written warning' come after 'verbal warnings', and it shows they've decided to fire you and this is your chance to quit to avoid being fired. If you're going to quit, of course you don't have to sign the warning.
The thing about written warnings is that you can never tell, from reading them, what the problem is! They usually include your whole job description--get to work on time, finish tasks in the allotted time, show up for meetings, follow orders, etc. etc. They do this so that after this if you mess up ONE TIME on ANYTHING, they can say 'you were warned about this'.
The last one of these I got, I tore it up in front of the boss's face. "Sure, I'll sign it." rip rip rip "Do you like my penmanship?" rip rip rip. 8^)
Bruce
Normal procedure is to request a signature so they have documentation that you received the discipline and to give you the opportunity to respond. Whether you sign it or not is a personal choice. Refusing does not invalidate the discipline, and it could strongly suggest you are not accepting responsibility.
StarShine
That depends on the laws where you work and your company's policies. Most people have employees sign write ups as confirmation that they were informed of the incident (and most have notes that signing only acknowledges that they were informed, not that they necessarily agree).
Where I've worked in the past, if the employee refused to sign, that was also noted on the write up.