The number of wage and salary workers who were union members dropped to 12 percent of the work force last year, the lowest percentage since the government started tracking that number over two decades ago.

The number of workers in a union was 20.1 percent in 1983, when Bureau of Labor Statistics first provided such comparable numbers, and that number has been declining steadily. More than a third of American workers, about 35 percent, were union members in the mid-1950s.

The continuing decline in union membership, documented in the BLS report released Thursday, comes as organized labor is pushing for legislation in the Democratic-controlled Congress making it easier for workers to form unions.

That proposal, called the Employee Free Choice Act, would let workers form unions more readily by simply signing a card or petition, impose stronger penalties on employers who violate labor laws, and allow for arbitration to settle first contract disputes.

Advocates of the legislation say they doubt that it will get signed into law by President Bush, but that they think passage in Congress would make eventual signing of the law more likely.

Supporters say the law is more fair to workers because employers can't mount a campaign to prevent formation of a union. Opponents say it deprives workers of the right to vote privately on their union preferences, and can lead to union intimidation of workers.

The union membership rate for government workers, 36.2 percent, was substantially higher than for private industry workers, 7.4 percent.