I run a small company (5 salaried employees). We have recently expanded from 3 to 5 staff, and while we are comfortable financially, there is not much spare money available. However there is a lot of work to do because the new staff are undergoing a significant amount of training.
A couple of employees are being overly persistent in working overtime to help meet the workload. I have asked them not to on numerous occasions but they insist! Or they say they won't, but go ahead and do it anyway.
If we could afford to pay them to for this overtime it would be great. But we can't, so I'm unhappy having them work extra hours for no pay. I'm extremely grateful to have such committed individuals on the team. But it makes me feel uncomfortable - for example, if things took a down turn and somebody had to leave, it could cause bad feeling if one of the 'overtimers' were dismissed.
I'm wondering what might be the best way of demonstrating my appreciation to these staff whilst firmly disallowing this type of behaviour?
Wow so many answers! Thank you. I marked MJ6's as the answer because this is the approach I actually used. There was some very useful stuff in the comments of that, unfortunately somebody has seen fit to remove these :(
You can see from the votes how many other great answers there are. And though it only has 2 votes (so far), I rate Adam Davies' answer highly because it addresses the core of the issue - how to be appreciative but firm.