While union membership is in decline, unions have been wooing rank and file at rival unions, the Los Angeles Times reported Saturday.
The Teamsters recently attempted to court members of the Transport Workers Union, which fought back with mailings of vomit bags to members and ads on billboards and in magazines.
In defense against a Teamsters union incursion, the Transport Workers Union churned out the slogan: "Teamster Air: More job departures to China than any other union."
Unions say they are recruiting rival union members because they want workers to have the best representation possible. But there are millions of dollars at stake, as well, the Times said.
Healthcare workers in the Service Employees International Union, for example, pay $51.74 per month in membership dues. That adds up to $28 million per year.
With greater numbers, a union also has more political clout, as unions can wield considerable influence on electoral politics and public policy.
In hard economic times, as layoffs and contract concessions mount up, union members become frustrated with their representation -- and unions, instead of finding non-union workers to recruit, tend to go after members of a rival union, the Times said.
"Generally speaking, we have seen these unions launch more raids and break more peace. It seems that the traditional breakdown is falling apart," said J. Justin Wilson, managing director for the Center for Union Facts, an anti-union group.
The National Union of Healthcare Workers recently attempted to persuade 45,000 healthcare workers with the Service Employees International Union to switch unions. Healthcare workers in Vermont were asked to choose between the SEIU and the American Federation of State, County and Municipal Employees, but SEIU pulled out before the election was held.
Rivalries between unions rise "in an environment in which there are givebacks, cutbacks, concessions in bargaining and the union movement is in retreat," said Nelson Lichtenstein, director of the Center for the Study of Work, Labor and Democracy at University of California, Santa Barbara.
"And when that discontent happens, they may look around for another or a better union," Lichtenstein said.
Notable deaths of 2014 [PHOTOS]