By Richard Cowan

WASHINGTON (Reuters) – Conservatives in the U.S. Congress who object to President Barack Obama’s immigration policies are threatening to tie a must-pass budget bill to the issue, making for a possible showdown in September and raising the specter of a government shutdown.

White House-Congress tensions rose on Wednesday when Obama spokesman Josh Earnest said the president’s upcoming decision on steps to possibly ease some immigration rules would not be affected by Republican tactics.

“The president is determined to act where House Republicans won’t,” Earnest said, citing support from the business community, religious leaders, labor unions and law enforcement. “It would be a real shame if Republicans were to engage in an effort to shut down the government over a commonsense solution (on immigration).”

When lawmakers return from their summer recess on Sept. 8, they hope to sprint to another long break beginning around Sept. 19. That gives them little time to agree on temporarily funding federal agencies on Oct. 1, the start of a new fiscal year.

One year ago, Congress faced a similar task. But Republican leaders’ plans for smooth passage of legislation disintegrated when Tea Party-backed lawmakers led by Senator Ted Cruz of Texas insisted on using the spending bill to gut Obama’s landmark healthcare program known as Obamacare.

Federal agencies were shut down for 16 days because of a lack of funds, before a bruised Republican Party relented.

Now, with partisanship running high ahead of November’s congressional elections, infighting over the spending bill – known as the continuing resolution, or CR – could become even more acute.

In part, that is because Congress left for recess unable to cut a deal on Obama’s request for emergency funds, which he said were needed to deal with an influx of Central American children illegally entering the country.

A spokeswoman for the White House budget office said the administration urges Congress to act on that request. Since most Republicans are opposed, it could spark a battle over the bigger bill to keep the government operating.

That would be nothing compared to the fight Obama could touch off in September if he announces unilateral actions giving temporary legal status and work permits to millions of undocumented residents.

Such a move could prompt some Republicans to retaliate by holding up the government-funding bill unless it prohibits Obama from carrying out immigration policy changes – a step Senate Democrats likely would oppose.

“If the president wields his pen and commits that unconstitutional act to legalize millions, I think that becomes something that is nearly political nuclear,” the Des Moines Register newspaper in Iowa quoted Republican Representative Steve King saying at a meeting of conservative Republicans.

Obama has said he will use his executive powers at the end of summer because Republicans have blocked changes to an antiquated, unworkable U.S. immigration law.

According to one Senate Republican aide, “The focus is on doing everything … to force Senate consideration” of a bill passed by the Republican-controlled House on Aug. 1.

That measure would reverse Obama’s 2012 policy giving temporary legal status to some undocumented residents who were brought to the United States as children years ago by their parents. It would also stop Obama from expanding the policy, possibly to parents of those children.

“An area of focus is the CR,” said the aide, who added that several senators are ready to join the effort.

But with Republicans on the verge of a November election win that could see them expand their majority in the House and capture the Senate, the last thing party leaders and many rank-and-file members want is to raise the possibility of a government shutdown – something voters do not tolerate.

At the same time, Democrats, according to congressional aides, will have to calculate whether they could be damaged in November by a September fight over immigration.

If either side blinks, there could be swift passage of a bare-bones temporary spending bill, delaying the showdown until after the elections.

In an interview this week with the conservative news and opinion website Breitbart, Republican Senator Marco Rubio of Florida backed using budget bills to roll back Obama’s immigration policies.

“There will have to be some sort of a budget vote or a continuing resolution vote, so I assume there will be some sort of a vote on this (immigration),” he said.

It’s an effort that could have the backing of the conservative group Heritage Action for America, where spokesman Dan Holler mulled the possibility of linking the urgently needed funding bill with language to stop Obama’s executive actions on immigration.

The immigration policy controversy, he said, is having “a freezing effect on what September looks like” in Washington.

(Additional reporting by Roberta Rampton and Julia Edwards; editing by Caren Bohan and Douglas Royalty)

• Politics & Government
• Government
• Barack Obama
• government shutdown