More than half the tax increase now awaiting Illinois Gov. Pat Quinn’s signature is supposed to be phased out after a few years. But the last time lawmakers passed an income tax hike that was “temporary,” it didn’t stay that way.

Short-term pain is easier to absorb than long-term pain. At least that’s how former Illinois Senate Pres. Phil Rock explains how he and then-Gov. Jim Thompson were able to sell two income tax increases in the 1980s.

“Everybody understood it was a temporary tax,” Rock said in an interview last year. “It was only going to hurt for a little while. Just like getting a shot: only one little jolt and it’s over.”

That second tax increase, though, didn’t end up being temporary; the legislature made it permanent before it expired.

Part of the income tax increase now awaiting Gov. Quinn’s action is supposed to disappear soon. Initially, the bill would raise the personal tax rate up from its current 3 percent, to 5 percent. In four years, it’s scheduled to drop to 3.75 percent.

But some Republicans warn that, just like two decades ago, temporary now doesn’t necessarily mean temporary later.

“I think that’s a cruel hoax to play on citizens who say this is temporary, when in reality it’s not,” said House Republican Leader Tom Cross of Oswego, following the House vote on Tuesday.

Cross claims Democrats will allow spending to keep growing, so that by 2015, the legislature won’t be able to let the tax rate drop.

“When are we going to figure out we can’t spend money we don’t have?” Cross said.

For his part, the governor on Wednesday defended the tax package. He said Illinois’ “fiscal house was burning.”

“This is a temporary income tax to deal with the immediate fiscal emergency our state faces,” Quinn told reporters.

Quinn would not say whether he would support making the increase permanent in a few years.

“Well, we’ll deal with one day at a time, one week, one month, one year at a time,” Quinn said.

That gives the governor something awfully important for any politician: wiggle room.