Can you elaborate on this? I've never heard of any legitimate situation where a person had to say they were single when filing taxes when in fact they were married. In fact, making such a false statement on official documentation is generally regarded as a crime. ("Under penalty of perjury, I swear that...", etc.)
Perhaps when you say "NOT able" you mean that you just don't want to, because of the financial consequences? If so, that's a really dumb idea that could quite easily come back to bite you in the ass.
It can potentially cause problems. But it may not. USCIS wants to see evidence that your marriage was entered into in good faith. Part of the evidence for that is proof of shared financial liability. There are many ways to give evidence of that shared liability. One is by filing taxes as "married, filing jointly". However, you don't have to do that; many couples are financially better off if they file as "married, filing separately" and I doubt that USCIS would hold it against someone for doing that, as long as they provide other evidence that establishes shared liability (e.g. having joint bank accounts, having both your names on an apartment lease, mortgage, car loan, etc.).Our accountant said that if we don't file as "married" then my husband will have problems when he eventually applies for Citizenship. That didn't sound true to me. Thoughts?
However, if you lie and file your taxes as "single" AND you didn't provide much in the way of solid proof of a genuine marriage from a financial perspective, that could certainly put your immigration status at risk (as well as your non-criminal status).

