WASHINGTON - With union membership on the decline, labor leaders are getting more creative - and some say more desperate - to boost sagging numbers and rebuild their waning clout.

Unions are helping non-union fast-food workers around the country hold strikes to protest low wages and poor working conditions. They are trying to organize home day-care workers, university graduate students and even newly legalized marijuana dealers. Members of a "shadow union" at Wal-Mart hold regular protests at the giant retailer, which long has been resistant to organizing.

Labor leaders say unions must create new models and new ways to represent workers to reverse a steady slide in the union ranks. Those efforts have taken on greater urgency since the Bureau of Labor Statistics reported earlier this year that union membership had declined to just 11.3 percent of the workforce - its lowest point in nearly a century.

"To be blunt, our basic system of workplace representation is failing to meet the needs of America's workers by every critical measure," AFL-CIO President Richard Trumka said in a recent speech.

The most high-profile tactic has seen hundreds of low-wage workers at McDonald's, Burger King and other fast-food chains walk off their jobs this week in a series of one-day strikes to demand better pay and the right to unionize. Workers are demanding wages of $15 an hour, more than double the current federal minimum wage of $7.25.

The actions in New York, Chicago, Detroit and other cities are being coordinated by local worker centers, nonprofit organizations made up of unions, clergy and other advocacy groups. While not technically labor groups, they receive generous financial support and training staff from the Service Employees International Union and other unions.

"Our primary goal is to help workers boost wages," SEIU President Mary Kay Henry said. "We think a key part of that is helping workers form organizations where they can directly bargain for wages with their employers."

Labor strategists say the fast-food campaign has long-term potential for unions. If unions can't organize through traditional methods, they see the smaller mobilizations through worker centers as a way to show low-wage workers how coordinated action can win some concessions from employers. That might make workers in the rapidly growing fast-food industry more sympathetic to the idea of joining a union later on.

"The fast-food and Wal-Mart strikes are exciting examples of workers reinventing the strike, going on offense and challenging inequality," said Stephen Lerner, a labor and community organizer and architect of the Justice for Janitors campaign in the late 1980s and early 1990s.

But the tactic has raised the concern of business groups, which say these organizations are merely "union fronts" designed to operate outside labor laws so they don't have to follow restrictions on secondary picketing, boycotts or file reports with the Labor Department. House Republicans wrote a letter to the Labor Department last week asking officials whether the groups need to abide by labor laws.

"An advantage of these groups is they allow unions to gain entry into a block of workers without them realizing this is just a front for a traditional union," said Glenn Spencer, vice president of the U.S. Chamber of Commerce's Workforce Freedom Initiative.

The number of worker centers has grown from five in the 1990s to more than 200 today, including the Restaurant Opportunity Center, National Day Laborers Organizing Network and the National Domestic Workers Alliance. The AFL-CIO and member unions are trying to leverage alliances with those groups, as well as progressive groups that have similar goals. At the AFL-CIO's convention in Los Angeles next month, the federation is expected to announce stronger partnerships with the NAACP, Hispanic advocacy groups and the Sierra Club.

"They advance organizing in the traditional sense, but also advance workers' interests in the more general sense," said Craig Becker, general counsel at the AFL-CIO.

Becker said the AFL-CIO hopes to create a broader and less formal kind of membership, which brings employees into the labor movement even if they don't work under a collective bargaining agreement. The AFL-CIO also wants to expand its Working America affiliate, which has more than 3 million members sympathetic to unions but who don't have a union at work and pay only token dues or nothing at all.

As businesses have become more aggressive and successful at battling union organizers, unions are also increasingly targeting nontraditional workers for membership. In Minnesota, lawmakers this year authorized unions to try organizing some 12,700 home day care providers whose care of children is subsidized by the state. Similar measures affect home care workers in Vermont and Rhode Island.

Unions claim collective bargaining will help home day care workers earn better wages and benefits for health care and retirement. But critics say the added costs will be borne by parents who can't afford it.

Unions also hope to target thousands of graduate students at private universities. Labor advocates are urging the National Labor Relations Board to overturn a 2004 decision that said graduate assistants are more like students than employees under federal labor laws.

The NLRB indicated last year that it would reconsider the question, and with the board's newly confirmed Democratic majority this week, unions may have a chance. Some universities are wary, though. Peter Weber, graduate school dean at Brown University, told lawmakers at a House hearing last year that unionizing grad students would "damage the fabric of graduate education."

One surprising area where unions have had success recently is organizing marijuana dealers in states that have legalized the drug for recreational or medical use. The United Food and Commercial Workers Union, the nation's largest union for retail workers, helped support ballot measures to legalize marijuana in Colorado and Washington last year and now counts about 3,000 members in the industry.