NEW YORK (CNNMoney.com) -- The United Auto Workers union launched a nationwide strike against General Motors on Monday as 73,000 UAW members walked off the job and hit the picket lines at the nation's largest automaker.

UAW President Ron Gettelfinger blasted GM management, saying that the company had not been willing to meet the union part way in negotiations.

"This is nothing we wanted," he said about the strike. "No one benefits in a strike. But there comes a point where someone can push you off a cliff. That's what happened here."

Company officials did not respond to Gettelfinger's comments, other than to say they were disappointed that the first national strike against the company in more than 37 years had been called, and that they hoped that an agreement to end the walkout could be reached soon.

Talks between the two sides resumed Monday afternoon after the union's press conference and continued more than five hours through the afternoon and into the evening before recessing for the night just before 8 p.m. Monday.

The same negotiators had been at the table in a marathon session that started early Sunday and went right up to the 11 a.m. ET start of the strike on Monday.

GM spokesman Tom Wickham said talks are expected to resume Tuesday morning, although he did not have any detail on when, and would not comment on progress made in the latest negotiations.

Gettelfinger said at the midday press conference that the union is ready to discuss the company's key bargaining goal of shifting an estimated $51 billion in healthcare expenses for retirees and their family members to union-controlled trust funds. But he said that other issues had derailed hopes of an agreement.

The union president said he was looking for assurances from the company about the job security of UAW members. He said he wanted guarantees about how much GM would invest in U.S. plants and about how many new vehicles would be built in the United States.

The UAW has seen its membership at GM plummet by 70 percent since 1994, as the automaker dumped its parts unit and closed plants to try to align its production more in line with its shrinking U.S. market share.

The strike halted operations at 80 facilities, ranging from assembly lines to parts distribution centers, in 30 states coast-to-coast. It also is likely to soon stop operations at GM plants in Canada and Mexico that depend on production from U.S. facilities, as well as the plants of many GM suppliers.

Still, most GM dealers won't start to see shortages of vehicles for two-to-three weeks, even though the strike will immediately halt production of 12,200 vehicles per day or 760 vehicles per hour, said Michael Robinet, vice president of global vehicle forecasts for CSM Worldwide. GM's inventory is above those of Japanese rivals and U.S. sales have been soft in recent months following the subprime mortgage meltdown, although GM bucked the trend to post a much better than expected sales month in August.

"Even if they have too much inventory, this is not a positive for the company," said Robinet. "I think they would rather take inventory out on their terms, not someone else's terms."

Picket signs went up at plants around the country just after 11 a.m. ET, followed by a stream of union members driving out of the plants' gates.

The workers had stayed on the job for nine days past the original expiration of the contract on Sept. 14, while union and management negotiators kept talking. But late Sunday night, the union set the strike deadline for 11 a.m.

The company said it was still hopeful it could reach a quick deal with the union, despite the start of the strike.

"We are disappointed in the UAW's decision to call a national strike," said a statement from GM. "The bargaining involved complex, difficult issues that affect the job security of our U.S. work force, and the long-term viability of the company. We are fully committed to working with the UAW to develop solutions together to address the competitive challenges facing General Motors. We will continue focusing our efforts on reaching an agreement as soon as possible."

Since the start of 2005, GM has taken a hit in its core North American auto unit, which posted nearly $13 billion in net losses in 2005 and 2006 combined. Losses continued in the first quarter of 2007 before the unit posted a narrow profit in the second quarter, but it was likely to report continued losses this year even without the costs associated with a strike.

The company has also seen its U.S sales fall along with its financial fortunes. It sold close to 1 in 3 cars purchased in the United States as recently as 1995. In the first eight months of 2007, its market share had fallen to less than 1 in 4 vehicles, or the loss of close to 10 percent of the market.

For his part, union boss Gettelfinger did not dismiss the notion that GM was in trouble. But he said there is only so much the union can do to stem losses at GM facilities.

"Obviously we're very concerned about this company," he said. "I remind everyone we've done a lot of things to help that company. But there comes a point in time we have to draw a line in the sand."

While the strike hit GM plants and facilities, it does not affect the two other automakers whose workers are represented by the UAW, Ford Motor (Charts, Fortune 500) or Chrysler LLC, which between them have more than 100,000 UAW still on the job. Members at those companies have been working under their own contract extensions as the union concentrated on reaching a deal with GM.

UAW strikers: Worried, but firm

A key to the contract talks is GM's goal of shifting an estimated $51 billion in future healthcare costs for retirees and their family members to union-controlled trust funds. GM has more than 340,000 retirees and surviving spouses receiving such benefits today.

Shifting those costs is seen as a key to GM efforts to close its cost gap with nonunion automakers, such as Toyota Motor (Charts) and Honda Motor (Charts). Ford and Chrysler combined are facing nearly $50 billion of retiree healthcare costs as well.

Gettelfinger disclosed that two years ago the union proposed setting up the kinds of trust funds, known by the accounting short-hand of VEBAs, that are now being sought by the company. Instead the company and union negotiated a less dramatic manner to limit the cost of retiree healthcare for the company. He said that if the company had taken the union's proposal at that time, it could have saved $1,000 per vehicle.

"They did raise the VEBA [in current talks] and we were more than eager to discuss it," Gettelfinger said. "Let me be very clear on this point - this strike is not about the VEBA in any way, shape or form."

Shares of Dow component GM (Charts, Fortune 500) closed down just 20 cents Monday, although that's well off of the 2.6 percent gain they were showing before the strike started.

Most analysts have said that although a long strike at General Motors would be a crippling blow for the automaker's efforts to return its North American operations to profitability, the automaker is probably in a relatively good position to weather a short strike.

David Healy, analyst with Burnham Securities, said he believes GM could take a strike of up to a month without a significant problem.

"It's sort of an odd thing, the first thing that happens with an automaker in case of a strike is their cash increases, as their payroll stops, and they still keep collecting cash for the cars that have been shipped," said Healy.

He believes the two sides are close enough that the strike will be a short one.

"Days, not weeks or months, that would be my guess," he said.

John Casesa, managing partner for New York auto consulting firm the Casesa Shapiro Group, also expects a short strike.

"I don't think the strike is simply for appearances. The UAW doesn't take a strike lightly," he said. "I do think there were stumbling blocks at the last minute. But given [Gettelfinger's comments about a trust fund], that's why I think they will eventually reach an agreement. This has been a topic of discussion around the union and GM for a couple of years."

Casesa said that it's possible that the strike could even make it easier for the union leadership to eventually win rank-and-file approval of any deal that is reached, which is necessary for a contract to be ratified.

"I think a short strike has the effect of sending a message to the more aggressive parts of the union that leadership is fighting for every dollar," said Casesa. "If it takes a couple of days strike to get the landmark agreement the two sides are talking about, that's a pretty small cost to pay."

Standard & Poor's, which has given junk bond status to GM's credit rating for more than two years, said it does not intend to further downgrade the company's debt unless the strike stretches on longer than what it expects to be "a brief and largely symbolic period."

But if the strike is longer than expected and causes more serious problems for GM's finances, it won't be alone in feeling the pain. In that case, the credit agency said that the ratings of certain GM suppliers would also be at risk of a downgrade.

The strike is the nation's largest since 87,000 workers at Verizon Communications (Charts, Fortune 500) walked off the job in August 2000, but that action did not shut down the company.

GM was last hit by a strike at its Flint, Mich., locals in 1998, a work stoppage by only 9,200 workers that was felt across most of GM's North American operations for 54 days since they couldn't get the parts they needed to keep making cars and trucks. The last true national strike against GM came in 1970, which lasted 69 days.

The last strike by more than 70,000 workers that shut down a company's operations was the 1997 strike by 185,000 Teamsters at United Parcel Service. (Charts, Fortune 500)