Top congressional Democrats officially introduced legislation Thursday to raise the federal minimum wage to $15 an hour by 2024, up from its current level of $7.25.

The move marks a stark policy change for the party, which was promoting an increase to just $10.50 as recently as 2015.

"What we are here today to say is that a living wage is $15... If you are working 40 or 50 hours a week, you should not be living in poverty," said Sen. Bernie Sanders, I-Vt. He noted it had been almost a decade since the last time Congress had raised the level.

Among those introducing the legislation were Senate Minority Leader Chuck Schumer of New York, House Minority Leader Nancy Pelosi of California, House Minority Whip Steny Hoyer of Maryland, Sen. Patty Murray of Washington and Rep. Bobby Scott of Virginia, the top Democrat on the Education and the Workforce Committee.

The legislation, called the Raise the Wage Act, would fully phase in the rate by 2024. It also would eliminate an exception for tipped workers. It has 35 co-sponsors in the Senate and 152 in the House.

The legislation is unlikely to go far in the Republican-controlled Congress, although some increase short of the $15 level is possible. President Trump has expressed openness to a level as high as $10, though at other times his comments suggested he would level the level untouched.

"We are here today to ask President Trump to stick up for working people by supporting our bill," Schumer said.

Increasing the federal minimum has long been a priority of the Democratic Party, although it traditionally has backed incremental increases. When the Obama administration's second-term proposal to raise the level to $10.10 got no traction in Congress, liberal groups decided to aim higher and started the $15 push. After resisting that idea for years, Democrats have fully embraced it, as Thursday press conference showed.

"What did they say about $15 an hour? Not gonna happen. Now you got Pelosi and Schumer, Sanders and Scott, the leadership of the Democratic caucuses in both houses, hand-in-hand, saying, 'We got to have $15,'" said Rep. Keith Ellison, D-Minn., deputy chairman of the Democratic National Committee.

Most economists say that higher minimum wages usually cause job losses, especially at the low-wage level, because small- and medium-sized businesses can't afford the higher labor costs. A national rate of $15 would more than double the current minimum wage, an unprecedented jump. The Congressional Budget Office estimated in a 2014 report that an increase to just $10.10 would cost 500,000 jobs.

The University of Washington, in a study commissioned by Seattle as part of the phase-in of its $15 minimum wage, found last year that an increase to $11 an hour had not benefited Seattle's low-wage workers. Instead, it resulted in modest declines to their employment rates and hours worked. While the workers did experience boosts in earnings overall, the report found that the increases would have happened without the higher minimum thanks to the region's growing economy.

The senators rejected the idea there would be any negative effects from a higher minimum wage. "This increase to the minimum wage is the biggest stimulus that we can give to the economy," Pelosi said, arguing the wages would lead to increased consumption.

Several Democrats said the real reason to back the legislation was not economic. "I think it will help the economy, but for me it is a moral issue," Schumer said.

The minimum wage push was mainly the work of organized labor, specifically the 2-million-member Service Employees International Union. It started out as a campaign directed at fast-food restaurants, which the union was trying to organize. "In 2014, SEIU International president Mary Kay Henry launched the 'Fast Food Forward' and 'Fight for 15' campaigns. The idea was simple: demand a living wage and the right to form a union without retaliation," wrote SEIU Local 775 President David Rolf, a key leader of the movement, in his 2016 book, The Fight for 15.

Unions support higher minimum wages because they create upward pressure to raise all wages and make non-union labor less economically competitive.

SEIU ran the most prominent groups involved in staging protests and other events, according to its Labor Department filings. It poured at least $14 million into the effort in 2016 alone. That includes $3.6 million to the Fast Food Workers Committee, the main group behind the "Fight For $15" movement, as well as nearly $9 million to various regional workers committees engaged in similar activism. Kendall Fells, the organizing director of Fight for $15, is listed in SEIU's filing as a "deputy organizing director" at a salary of $146,000.

The effort had little success in organizing restaurants but gained support with Democrats in liberal West Coast cities. Seattle-Tacoma was the first municipality to adopt the wage in 2013. It was followed by Los Angeles and San Francisco in 2015. Those city ordinances all included exemptions for businesses with collective bargaining agreements, provided their unions went along. The exemption gave businesses a strong incentive to allow unions since it meant they could potentially pay their workers less than the new minimum wage. Such exemptions were not included in later campaigns after they attracted bad press for the activists.

The minimum wage effort eventually reached the state level with California and New York both adopting a $15 rate last year. Nevertheless, top Democrats were wary. Hillary Clinton officially backed a $12 minimum wage during her presidential campaign. "Substantively, we have not supported $15 — you will get a fair number of liberal economists who will say it will lose jobs," Neera Tanden, head of the liberal Center for American Progress and a top adviser to Clinton's campaign, told other staffers in an April 2015 email that was made public by WikiLeaks. Clinton's campaign went to considerable effort behind the scenes to avoid having to discuss the issue.

Nevertheless, Democrats felt increasing pressure to back the rate after Sanders' unexpectedly strong challenge to Clinton in the 2016 presidential campaign. Clinton clouded the issue by backing some local $15 efforts and by announcing in one debate that, if elected, she would sign legislation for a $15 rate. Later that year, the Democratic National Committee officially adopted a $15 rate as one of its platforms.

The DNC has apparently had a hard time living up to its own rhetoric. A class-action lawsuit filed in Pennsylvania charges that the DNC, the Pennsylvania Democratic Party and others involved in the party's 2016 national convention failed to pay overtime wages to an estimated 50 national field organizers.