How to negotiate severance?

I just posted yesterday about how I was let go at J1. I have also been misclassified as a 1099 when they treated me as an employee.

This job only gave me a 1 week severance. I am wanting to negotiate a higher severance package to help cover my tax bill since I was misclassified as a 1099.

If I email them stating the above and then adding something in that states “If we are unable to reach a satisfactory resolution, I may be compelled to file Form SS-8 with the IRS to clarify my employment status and Form 8919 to report my uncollected Social Security and Medicare taxes” what tare the chances they will give me a higher severance?

They still have at least 4 other employees that are being paid via 1099 that also should be W-2. If the IRS gets involved, they are going to be caught doing the same to them as well.

Just looking for advice from my fellow OEers!