Ronald Reagan's presidency signaled a critical period for organized labor, a time when unions began shrinking at a much faster pace and it became more acceptable for businesses to fight off labor organizations.

But what remains in dispute about his legacy is whether the former president's actions triggered a decline in union membership or accelerated a trend that was had already begun.

"It isn't clear whether Reagan set the tone for the '80s and into the '90s, or whether he reflected changes in society," said Charles Craver, a labor law professor at George Washington University Law School and author of Can Unions Survive? The Rejuvenation of the American Labor Movement.

The percentage of the American work force that was unionized peaked in the 1950s at about 35 percent and had fallen to 23 percent by the time Reagan was elected in 1980, according to Craver and the Bureau of Labor Statistics.

During the decades leading up to Reagan's presidency, the number of union members grew - but not as quickly as the work force was expanding.

The culture had started to change, America was becoming more conservative, and employers were becoming more strongly anti-union, Craver said.

An important turning point came in 1981, shortly after Reagan took office, when he fired about 12,000 federal air traffic controllers who went out on strike.

The controllers - represented by one of the few unions that supported Reagan in his bid for presidency, the Professional Air Traffic Controllers' Organization or PATCO - were fired for violating a law that forbids federal workers from striking.

By carrying out his threat to fire the controllers if they did not return to work Reagan not only set limits for public employee unions, but also signaled that it was OK for businesses to play hardball with private sector unions.

'Sent a message'

"The biggest thing that that did was it sent a message to the private employer community that it would be all right to go up against the unions," Craver said. "Whether he intended to do that, I don't know."

After the PATCO strike, the number of union members began to decline.

Only about 12.9 percent of workers belonged to a union last year, according to the most recent numbers available from the Bureau of Labor Statistics.

"Beginning in the '70s you started to have a number of corporations who began to challenge labor, not just at the negotiating table, began to challenge the legitimacy of organized labor," said John Jordan, president of Washington public relations firm Principor Communications and a union organizer for 10 years.

'Opened floodgates'

"This really didn't become mainstream acceptable until Reagan broke the PATCO union, and that really opened the floodgates to a major effort on the part of corporate America to essentially beat labor back into a corner to a place where they haven't recovered yet," said Jordan.

The National Air Traffic Controllers Association, which was formed to represent the controllers after PATCO was broken in the strike, declined to comment on Reagan this week other than to offer condolences to his family.

Ironically, Reagan served as president of the Screen Actors Guild from 1947 to 1952 and then again in 1959 for a year.

Some industry experts said the criticism he received during and after the PATCO strike was undeserved.