Talks between The Boston Globe and its unions to prevent the U.S. newspaper from shutting down stopped early Monday morning after a midnight deadline passed, and it was unclear when they would resume.

An hour after the midnight deadline passed, negotiations had broken down, but likely will resume sometime during the night, a source familiar with the matter, but not authorized to discuss it, told Reuters.

That source and another source familiar with the matter indicated that the bargaining process likely will continue throughout the night, and that word on a decision about what will happen to the Globe will wait until after daybreak in the United States.

Just before the deadline, the Globe's parent company, The New York Times Co, ratcheted up the pressure on unions at the Globe, threatening to close the paper within weeks if they do not deliver big cost cuts.

The Times, the Globe's parent company, said it would file a notice with the U.S. government on Monday that says it will shut down the paper if it cannot get millions of dollars in concessions from its unions.

It had set a Sunday midnight deadline for four unions to find $20 million in cost cuts at the Globe. Earlier it had set Friday as the deadline, but extended it after reporting Saturday that it had made progress.

If the Globe's management and the unions fail to reach an agreement, one of the most well known and largest U.S. newspapers could close, leaving Boston without a daily, full-service general newspaper of comparable size.

The 137-year-old Globe is a mainstay of New England news consumers. The paper is the 17th largest in the United States by daily paid circulation, according to the U.S. Audit Bureau of Circulations. On Sundays, a day that many U.S. residents spend reading their papers, it ranks 13th.

The Times said it would file notice under the Workers Readjustment and Retraining Notification act, which requires 60 days advance notice before closing a business. The move is the toughest pressure yet that the Times has applied.

Filing the WARN notice is a difficult step that we would like to avoid, said a statement issued by the Globe. But, unfortunately, given the state of the negotiations, it is one we must be prepared to take.

The Globe was once one of the top U.S. papers in its scope, with a strong international, national and local reporting staff that rivaled that of the biggest U.S. dailies, including The Washington Post, The Wall Street Journal, USA Today and The New York Times.

In recent years it was forced to cut back on operations, as advertising declines that have affected nearly every U.S. paper

hit the Globe particularly hard.

The Boston Newspaper Guild, the Globe's biggest union, said earlier Sunday evening that it proposed cuts that exceed the $10 million that the Times has demanded of it.

This proposal was the product of arduous deliberations, a guild statement said, calling its offers tremendous sacrifices. It declined to make details available until its members had a chance to review them.

Negotiations have become tangled over some benefits that the Times wants to erase, including some lifetime job guarantees, the Globe reported on its website on Sunday.

Management has told the leaders of three of the paper's major unions to enter negotiations or receive a message from the company, The Globe quoted union officials as saying in an article on its website Sunday night.

The Boston Herald reported that large numbers of layoffs could be on the table. The Guild, pressmen and mailers unions have some members with lifetime job guarantees.

The Globe wants $10 million in concessions from the Boston Newspaper Guild, its largest union, with the balance coming from the others.

The Times said the paper would lose $85 million this year and the cuts were essential to keeping the Globe open.

The guild said it is optimistic that the Times Co is genuinely committed to reaching agreement.

The Boston Newspaper Guild is one of the largest of about a dozen unions at the Globe, and represents about 600 people in editorial, advertising and other business roles.

While The Times and the union cited progress, the deadline extension came after the union said the Times Co made a math error that would result in the union having to make bigger sacrifices.

(Reporting by Robert MacMillan; Editing by Maureen Bavdek, Richard Chang and Kim Coghill)