About 2,000 nurses, community activists and others called on Detroit officials Friday to stop shutting off water to thousands of customers who are behind on their bills.

Protesters trying to prevent crews from conducting the shutoffs also picketed earlier in the day outside the offices of a private contractor working for the city.

The water issue gained national attention last month after activists appealed to the United Nations for assistance, and is a pending issue as the city prepares for an August trial on the largest municipal bankruptcy in U.S. history.

"Depriving Detroit residents of water they need cannot be condoned in a civilized society," said Jean Ross of National Nurses United, the group leading the demonstration through several blocks of downtown that included the chant, "Whose water? Our water!"

The protest drew both U.S. Rep. John Conyers, who is seeking a 26th term in Congress, his challenger, the Rev. Horace Sheffield III, and actor Mark Ruffalo.

Detroit's Water and Sewerage Department serves about 4 million people in the city and nearby communities. Kevyn Orr, the state-appointed emergency manager for Detroit, has said about $6 billion of the city's $18 billion debt load belongs to the water department, whose debt is generally expected to be paid off through customer billings.

Detroit has roughly 170,000 residential water customers, with more than 50 percent of those accounts delinquent by at least 60 days or $150. As of the end of June, nearly $90 million was owed on almost 92,000 past due accounts — including more than $43 million from Detroit households and nearly $21 million by businesses inside the city.

The city-owned utility stepped up the shutoffs in March and doesn't plan to stop.

Water department spokesman Bill Johnson said the utility "put customers on notice" that it expected them to pay their bills once the temperature rose above freezing.

"We have a responsibility to all the people in Detroit who we deliver water to, to make sure we collect the money so we can continue to make the necessary repairs and protect the integrity of this water system," said Johnson.

About 17,000 customers were on payment plans as of last month. "Anyone who came to us with a legitimate problem we put on a payment plan," Johnson said.

Some residents whose water was shut off said they had not received any notice.

In June, the water department shut off service to about 7,200 homes and businesses, but later restored it to about 3,100 customers who paid their bills or worked out payment plans. That 7,200 compares with about 1,570 in June 2013.

Service was shut off to nearly 4,600 customers in May and about 3,000 in April. Water was restored to more than 2,300 customers in May and more than 1,800 in April.

Some groups appealed to the United Nations for support in an effort to force the restoration of service. Three U.N. experts last month responded that the shutoffs could constitute a violation of the human right to water, but what the global organization might do beyond that is unclear.

Bankruptcy Judge Steven Rhodes told city officials this week that the shutoffs are causing anger and bad publicity. He told a water department official to return to court Monday with more options for people who can't pay.

City Hall needs to take a stand and call off the shutoffs, Conyers told The Associated Press.

"Then we have to work out a payment plan for those who actually owe money and want to make up for it," he said.

Detroit resident Brenda Flowers, who was among the marchers, said the fight now is "bigger than just Detroit."

"It's national now," she said. "You have people from all around coming here to support Detroit. If we continue to stand together and fight for this, I believe the federal judge will make them stop cutting this water off."