JEFFERSON CITY, Mo. (AP) — Not content to target only public-sector unions, Republican lawmakers in more than one-quarter of the states this year launched their most ambitious attempt in about generation to break up union shops in factories, offices and other private-sector workplaces.

But their efforts have largely faltered, in part because of opposition from fellow Republicans concerned that pushing too hard against unions could jeopardize other aspects of the pro-business agenda they staked out after strong statehouse gains in the 2010 elections.

Of the 14 states where "right-to-work" bills barring mandatory union fees were considered, only New Hampshire has passed the legislation, and it is uncertain whether Republican lawmakers can overcome an expected veto by the Democratic governor.