The Greens are slamming SkyCity over its convention centre cost blowout.

The casino firm has revealed a $130 million jump in costs for the centre it's building in Auckland, as part of a deal with the Government.

Greens spokeswoman Denise Roche says it's beyond belief cost increases weren't considered in the deal.

"Coming back to the government cap-in-hand is just unacceptable," she says.

They're still makes huge profits, and the stand to make more profit."

Denise Roche says SkyCity should suck it up, and swallow the cost increases.