The union that represents U.S. Immigration and Customs Enforcement officers says on at least two occasions last month two federal ICE employees called Portland police while being harassed by protesters—but cops did not show up, because Portland's mayor had ordered them not to intervene.

Members of the union, called the National ICE Council, sent Mayor Ted Wheeler a cease and desist letter Monday demanding he require Portland police to assist federal agents if called upon.

The letter, filed this morning by the union on behalf of employees working in Portland's ICE office, says Wheeler's decision to order Portland police not to assist federal agents was a violation of the U.S. Constitution. Specifically, it cites the 14th Amendment, which says the government cannot deny any person equal protection under the law.

"Your current policy forbidding Portland law enforcement agencies from assisting employees of the Immigration and Customs Enforcement Agency who request law enforcement assistance while at or away from work is a violation of the United States Constitution's Equal Protection Clause," the letter says.

ICE is a scorned agency in Portland, especially in the wake of a White House policy of separating immigrant families at the U.S. border. A protest camp blockaded and harried the Portland ICE office for more than a month. The camp was abandoned and swept by police July 25.

But the letter places a new legal demand on Wheeler. It says that if he does not allow Portland police to assist federal immigration agents from here on out, the ICE union will take him to court.

"We understand that you have a difference of opinion with the current President of the United States, and some of his policies, but we fail to see why targeting the employees of ICE and leaving them vulnerable to violence, harassment and even death furthers a legitimate government interest," their attorney, Sean Riddell, says in the letter. "Your policy has created a zone of terror and lawlessness."

The Portland Police Bureau deferred any comment on the dispute to the mayor's office. The mayor's spokeswoman Sophia June says legal counsel is reviewing the letter.

The people seeking relief in the letter are a local immigration agent and a representative from the federal agency's national office speaking on behalf of the union.

A local ICE officer, who spoke to WW only on the condition of anonymity, says two agency employees called Portland police June 19, when they were blocked from leaving the building in their vehicles. One of those employees told Portland police that protesters followed his truck as he went to pick up his daughter from summer camp and harassed him in the parking lot.

He also says protesters showed up at his Portland apartment building a few hours later. Again, he called police, but says no officer responded.

"This area became like a Wild West," the local immigration officer tells WW.

An email obtained by WW shows police defending their decision to federal officials.

Portland Police Deputy Chief Bob Day wrote the email June 19, replying to a formal request for assistance from the Federal Protective Service, a police division within the Department of Homeland Security. "At this time I am denying your request for additional resources from PPB," Day wrote. "I recognize this is a fluid situation that will need continuous monitoring. I am willing to revisit this inquiry after you have exhausted all alternative options besides arrests and maximized the use of FPS resources. We will respond to [calls] for assistance if your officers are assaulted and need us to facilitate a safe exit from the conflict."

Chris Crane, president of the national union, says the situation at the ICE building in Portland spiraled out of control because police would not assist federal agents.

"Every person in law enforcement knows there are few things as dangerous or as unpredictable as an angry mob," Crane says. "No one could have responded quickly enough to protect our employees who were trapped inside this building. All of this because the mayor of Portland has a beef with the president of the United States."

Wheeler opposes President Donald Trump's immigration policies, which he called "un-American" shortly after the Occupy ICE camp sprang up outside the federal building.

Trump administration officials have threatened in speeches and interviews to criminally prosecute mayors like Wheeler, who support local sanctuary laws and policies that sometimes shield undocumented immigrants from deportation.

Protesters surrounded the ICE building beginning June 17, after news reports about the federal family separation policy. The protesters briefly shut down the ICE building by blocking the entrances and exits, harassing employees as they arrived and attempted to leave. The occupation inspired similar protests nationwide.

Most of the camp remained peaceful. It broke down last week, after Wheeler sent a notice to protesters telling them he planned to sweep the camp because it was unsafe and he feared violence from far-right activists.

In their cease and desist letter, the ICE agents say Portland police put federal employees in danger.

"We ask that you end your policy of not responding to calls for police services from ICE employees immediately," the ICE union pleads in the letter to the mayor. "We would like to avoid federal litigation, but we are prepared to protect our membership and their families."

UPDATE 7/31/18: This post has been updated with additional information about communication between federal officials and Portland police.