Today my employer approached me to work this weekend. Normally I do not have an issue with this, but this will be my 3rd weekend in a row without a single day off. I informed my employer I would be unable to meet their request and their response was they addressed this with HR and I will be written up for being insubordinate.

My position is typically Monday to Friday 9-5. I am salary non-exempt so I do not get any compensation for working the weekends which does not bother because I know my work helps the company as a whole. My employer does not have anything posted regarding weekend coverage and no policies have ever been written.

Can they require me to work and have written disciplinary action taken? I have been with this company for 6 years with outstanding service but after this I feel I need to look for a new job.

Yes, they can require you to work and yes, they can write you up for refusing. Neither Federal nor PA law limits the number of days in a row you can be required to work.

However, if you are non-exempt they are required to pay you overtime if you work more than 40 hours in a week, regardless of whether you are generally paid on a salaried basis or not.