I urge you to secure more specific information regarding your plan. Sec 404(c) refers to certain negotiated plans and your reference to union contracts suggests that this may not be a typical plan most of us are familiar with. To add to the confusion, Sec 404(c) of ERISA refers to measures an employer can use to avoid liability for plan investment decisions under ERISA, which is an entirely different issue.
Also, note that if you are married this year, your tax filing status for the entire year will be married, typically filing jointly. If you file jointly, different income limits apply for Roth IRA contributions, and you both are subject to the same income limit. Regular Roth contributions enter the phaseout range at 178k of modified AGI and contributions are eliminated a 188k. If this happens, you can either remove the contributions or recharaterize them as non deductible TIRA contributions, and perhaps use the back door Roth strategy from there.