The nation’s union membership rate continued a decades-long slide last year, falling to 11.8 percent of the American work force in 2011, the Bureau of Labor Statistics announced in a report on Friday.

That was down from 11.9 percent the previous year even though total union membership edged up, rising by 49,000 last year to 14.76 million. The overall membership rate declined because the increases in organized labor’s ranks did not keep pace with overall growth in employment.

The bureau announced these numbers as the nation’s labor unions have been coming under heavy political attack. Republican governors and Republican-controlled legislatures in Wisconsin and in several other states have pushed to curb the power of public employees to bargain collectively. Moreover, Indiana is poised to become the first state in more than a decade to enact a “right to work” law, which bans employers and unions from agreeing to contracts that require workers to pay fees for union representation.

According to the bureau, 16.3 million workers are represented by unions, some 1.5 million more than the total membership, indicating that many workers opt out of joining the unions that represent them at their workplaces.