I understand that job duties can be added at employer will, and I accept that, but this one has me in a tizzy...
...I accepted a job 3 years ago and negotiated salary based on the fact that I would not be doing a specific duty. I was assured the company had other resources to take care of these duties so I negotiated my salary as such (if I am responsible for this, I want more. If I'm not, I'll take less.)
Fast forward a couple years, now I'm doing these duties because the other resources do not complete the tasks at hand or bill us for work being done on site or after hours. I'm being asked to do these jobs to 'save the company a buck', yet I am declining responsibility because I was told I would need to worry about it plus took a lower salary because I shouldn't be doing it in the first place. The money I've been saving them has been huge in some cases, so I asked for a slice of the pie to compensate for my time and fixing what our resource has broken.
I've made this issue clear with management and asked for a raise to reflect this, but I get responses like "That's out of our budget, why can't you do that?" which is frustrating because they know why. I'm not the guy who should be doing this. Just because our resource isn't doing it's job, why should I be responsible for picking up their slack when I was told I wouldn't have to? I've been more than patient with them on this, but it's affecting my work quality because I'm doing 30-40% of their job and 60-70% of mine. I feel like I've been lied to and they are just going to make me deal with it. They're ignoring the issues at hand and I'm eating their mistakes basically. I've asked them to bring someone on site to take care of these duties but they can't adjust the budget or have some excuse....
How can I respond to make it clear that I expect a higher wage since this is contrary to the scope in which I hired?