Anti-tax advocate Grover Norquist gave his approval Wednesday to the House Republicans’ “plan B” approach to allow tax rates to go up on household income above $1 million, even as other conservative groups condemned the plan and urged GOP lawmakers to vote “no.”

The message from Norquist’s organization, Americans for Tax Reform, gives some measure of political cover to lawmakers who have signed on to what the group calls its “pledge” to stand against any measure it interprets as a tax increase. Echoing statements by Boehner aides, Norquist said the measure (H J Res 66), which is scheduled for a vote Thursday, would simply prevent a scheduled tax increase from taking hold on most Americans, even though tax cuts for those beyond $1 million would expire.

But two other major conservative groups, Heritage Action for America and the Club for Growth, issued sharply worded attacks on the plan and said the Thursday vote would be a “key” vote counted in rating members of Congress.

“Allowing a tax increase to hit a certain segment of Americans and small businesses is not a solution, it is a political ploy,” Heritage wrote in statement. It would “constitute a clear path toward surrender on conservative principles,” it said.

Boehner, in the past week, has given ground to the White House in negotiations over the expiring 2001 and 2003 tax cuts (PL 107-16, PL 108-27). The Ohio Republican now says he would allow the cuts to expire only for households reporting more than $1 million in annual income, after first saying he would only accept new revenue by closing tax breaks.

Boehner’s aides and some lawmakers have said that would not mean a vote for a tax increase because the plan Boehner unveiled this week would not allow a scheduled tax increase to take effect for most earners. Norquist effectively endorsed that view with his statement.

The legislation “permanently prevents a tax increase on families making less than $1 million per year. Republicans supporting this bill are this week affirming to their constituents in writing that this bill — the sole purpose of which is to prevent tax increases — is consistent with the pledge they made to them,” the group said.

Nearly all House Republicans have signed a pledge created by Norquist against raising revenue by either increasing rates or curbing tax breaks.

On the surface, it appears the ATR’s conclusion also would apply to a White House offer that preserves the tax cuts for all income levels up to $400,000 and, perhaps, to a Senate-passed measure that set a $250,000 threshold for continuing the tax cuts.

The Club for Growth, a key group for congressional Republicans, blasted that logic in its statement.

“We don’t buy into the Washington-speak, suggesting that these are actually tax cuts,” Club for Growth Vice President Andrew Roth said.