The move could amount to a negotiating ploy to extract further concessions from the Globe’s unions, since the notice does not require the Times Co. to close the paper after 60 days. Talks between the two sides continued early today, wire services reported, after a midnight deadline to forge an agreement came and went. The threat of a shutdown puts the unions under fierce pressure to produce additional savings; the Boston Newspaper Guild promptly called the step a “bullying” tactic by the company.