'Martin' Star Tisha Campbell -- $400k Lawsuit Over STUPID Home Loan

Daaaamn Gina ... you owe a TON of money to the bank ... this according to a new lawsuit obtained by TMZ.

"Martin" star Tisha Campbell and her husband Duane Martin have been sued by City National Bank for more than $430k ... over a stupid home equity loan the couple took out in 2008 ... right when the housing bubble was bursting.

According to legal docs obtained by TMZ ... Tisha and Duane (an actor who starred in the ill-fated "Paul Reiser Show") took out a $625k home equity loan on a slick waterfront property in Lake Arrowhead, CA .

However, at the time of the loan the couple still owed more than $730,000 on their mortgage to ANOTHER financial institution -- Aurora Bank.

Long story short -- Tisha and Duane allegedly defaulted on BOTH loans. Earlier this year, Aurora foreclosed on the home ... and according to the docs, the bank sold it at auction for $925k.

Aurora got paid first ... and sent the remaining $192k to CNS to partially satisfy the home equity loan, which had already ballooned to $633,119.52.

City National is now going after Tisha and Duane for the balance ... plus interest.

But Tisha and Duane are PISSED -- a rep for the couple tells TMZ ... CNS is just trying to "bully" them for money they shouldn't have to pay.

The rep points out that CNS received a $400 million government subsidy in 2009 to help people like the Tisha and Duane through the mortgage crisis ... and says, "In this case City National refused to share the significant benefit that they received with the Martins."

The Martins are now threatening legal action against the bank -- claiming the bank discriminated against them.