Terrence Howard preparing to do battle with ex-wife Michelle ... trying to put a quick end to her spousal support because she allegedly blackmailed him with pics and videos he feared would ruin his career.

Sources familiar with the case tell TMZ ... Terrence will likely make a formal legal claim in April, alleging he gave Michelle a ridiculously rich spousal support deal because she was threatening him with various photos and videos.

We're told one of the pics shows Terrence in the shower, but there are many others.

The "Empire" star and lawyer Brian Kramer claim all Michelle was really entitled to was half-a-year's worth of spousal support, since the marriage lasted 1 year and the standard is to limit such support to half the time of the marriage. She got 5 years worth of support, which he says is evidence of blackmail

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