The resolution — which was adopted by the Service Employees International Union board on Thursday and was expected to be considered by the American Federation board in June — also would need to be ratified at conventions the unions have scheduled for this year.

The American Federation of State, County and Municipal Employees has 1.6 million members, most of whom are government workers. The Service Employees International Union has approximately two million members and is split nearly evenly between workers in the private and public sectors. About 80 percent of the unions’ membership is in roughly a dozen states, including New York, California and Illinois.

The purpose of the new arrangement, said Mary Kay Henry, the Service Employees International Union president, was to “unite the power of our organizations at every level to deal with the unprecedented attack on working people and growing inequality in this country.”

The unions plan “unity partnerships” to expand on such initiatives as a joint organizing drive of home-care workers, like a recent one in Pennsylvania, and joint lobbying efforts to persuade state lawmakers to increase funding for public schools and hospitals.

The benefits of the arrangement, officials said, would be that the unions could settle on common messages and strategies rather than tugging in different directions, and they could eliminate duplication of fixed costs — for phone banks, direct mail and advertisements. Union officials also said they hoped the joint efforts would prevent politicians from playing one union against the other when raising money for their campaigns, a practice the unions said they found exasperating but were often powerless to stop.