OKLAHOMA CITY, Oklahoma - Education groups are calling for a boycott of businesses that are helping collect signatures to stop the upcoming tax increase for teacher pay raises.

The group Oklahoma Taxpayers Unite is leading the charge on the veto referendum.

At first, they had a list of participating businesses on their website. Now, the group said they've removed it because of the backlash.

Critics argue that collecting signatures without a petitioner to witness is illegal.

"Somebody is supposed to witness the signature and then on the back has to attest in front of a notary that they witnessed all these signatures and all these are in fact registered voters," said Mickey Thompson with Restore Oklahoma Now. 

At least two education advocacy groups have filed legal challenges to this petition that will be considered in the Oklahoma Supreme Court.