As teachers inch closer to a walkout on April 2, it's worth looking back at the state question that ultimately made it very difficult, if not impossible, for Oklahoma legislators to pass legislation that would raise revenue.

It was State Question 640, which was approved by Oklahomans in 1992 and severely limits the Legislature's ability to raise taxes.

"Any tax increase that passed the House and Senate with less than a 3/4 majority would have to go to a vote of the people during the next general election," said News 9 reporter Mike Carpenter in 1992.

The measure was championed by stockbroker Dan Brown, president of a group called the Oklahoma Taxpayers Union.

"The intent is to force the Legislature to look at the the revenue that have already been given, that they are stewards of," he said.

Watch these reports from former News 9 reporters Mike Carpenter and Kym Koch, and follow along with our coverage of the current situation involving Oklahoma school teachers on our 'School Shutdown' page.