WASHINGTON (AP) — One of the nation's largest unions and a Democratic super PAC supporting President Barack Obama launched a joint $4 million Spanish-language advertising campaign on Monday, targeting Hispanic voters.

The ads, sponsored by the Service Employees International Union and Priorities USA Action, argue that Republican presidential candidate Mitt Romney's policies would benefit the wealthiest Americans at the expense of Hispanics and other working families.

Priorities USA Action, founded by two former Obama White House aides, has struggled in fundraising compared with Republican-leaning super PACs like American Crossroads and its nonprofit arm, Crossroads GPS. But the super PAC's partnerships with SEIU and other organizations, including the League of Conservation Voters and the United Auto Workers, help the group compete with the better funded GOP-leaning political action committees.