The correspondence has come to light after a long-running legal battle between the company and a union angry at being prevented from organising among Starbucks' 150,000-strong army of "baristas" and other employees.

The revelations come at a sensitive time, threatening to tarnish the chain's public image just as its pioneering chief executive, Howard Schultz, is trying to re-energise the company and attract customers back to its coffee shops.

In one email exchange, managers sought information about a Halloween party attended by employees, and reported how two people at the party had a discussion about union organisation. The conversation ended, one manager noted, because the two employees "were attracted to each other and this became the focus of their evening".

Starbucks says it does not prevent employees from organising into unions, they just don't want to. It has been fighting what it calls "disruptive" activity by the Industrial Workers of the World union since at least 2004, the emails make clear. "Below is a summary of the recent developments in New York City regarding our attempts to thwart a potential union situation," one three-year-old email begins.

The correspondence – leaked to The Wall Street Journal – came to light just days after Mr Schultz returned to the post of chief executive at the company he turned from a tiny Seattle business with just four stores into a global phenomenon. He has promised to put staff at the heart of a plan to revitalise the firm.

In a letter to employees and customers posted on the Starbucks website after his appointment, Mr Schultz wrote how he had "brought Starbucks to life" by hiring "an exceptionally engaged group of partners (employees) who shared our excitement about building a different kind of company. In doing this, we developed a culture based on treating each other, our customers and our coffee growers with respect and dignity."

Yesterday, a company spokesman said Starbucks abided by all labour laws, such as those that ban a company for firing employees for union sympathies. He said Starbucks was confident it would prevail in its legal dispute with IWW supporters claiming wrongful dismissal. The dispute "focused on enforcement of Starbucks dress code and [union lapel] pin policies, and partner disciplinary actions", he said. "These documents have been presented out of context and in vio-lation of a judge's orders."

The emails show that managers monitored a Cornell university alumni discussion board to identify employees that had graduated from a labour programme at the university, and they discuss when identified "IWW supporters" are next up for an appraisal and whether they might be at risk of firing.

According to the WSJ, managers several times expressed concern that emails could turn up in a legal case. In one 2005 email, a manager wrote: "Not to sound too 007 here but I am going to ask that we delete these messages after reading and stick to verbal conversations as none of this is protected under attorney client privilege and is subject to full disclosure."