One of the agencies targeted by the GMB (Britain's general union) has said it will take legal action against the organisation if the union again hampers its ability to provide staff.

The GMB said Bond Personnel (BP), a Wigan-based firm which supplied staff to JJB Sports in the summer, had provided staff as cover during strikes.

The GMB held demonstrations outside the offices of recruiters in the town, including BP.

BP and other two agencies involved — Heads Recruitment and Lightyear Recruitment — have since been cleared by the Department of Trade and Industry (DTI) of any wrongdoing. The company's managing director, Kate Bond, said she may call in the lawyers if BP is targeted again.

"The GMB were very aggressive with us from the beginning. How can they put out information about us and act in the way that they have? We feel bullied," she said. "I would consider legal action if this sort of thing happens again."

However, the managing director of Heads Recruitment, said that going to court is a big step that often comes too late anyway. Chris Gorton told Recruiter: "The damage is done by the time you go to court. If you think what you have to do, it could take a long time to convince a judge you're right."

Talks in mid-December between the GMB and JJB Sports averted further strike action early in the new year.

Despite the DTI's findings, the GMB said it may still pursue the matter through the courts. A spokesman told Recruiter: "We are looking to see if there are any legal options which remain open to us."

Gorton said unions should change their philosophy to improve their relationship with agencies. "Currently unions start off with the assumption that everybody is breaking the rules rather than believing everyone is working within the rules," he said.

Tom Hadley, director of external relations at the Recruitment and Employment Confederation, which advised BP throughout the investigation, told Recruiter: "This is a bit of a slap in the face for the GMB, after all the stuff they put out about these three agencies and the actions they took."

Hadley warned that unions could continue to cause problems for agencies and added: "We cannot be complacent. Unions certainly seem to be targeting agencies and it looks set to carry on — it's a big part of their campaign."

However, Hadley stopped short of suggesting that there was a cross-union bid to hit recruiters, and a spokeswoman for the Transport and General Workers' Union (T&G) told Recruiter: "We refute any suggestion of a cross-union drive. What we do is act against agencies who we think are breaking the law."

She spoke as drivers at the Iceland distribution depot in Enfield were on strike.

The union claimed that contractor DHL Exel used agency labour while the strike was on. As yet, the union has not named any agencies it believes were helping to break the strike.

Bodies in the public sector have also been coming under fire from unions recently.

Last month, the GMB wrote to local councils asking them to curb spending on agency staff, which it claimed provide "bad value for money" . A total of 434 UK councils said they spent £1.546bn on agency and temporary staff in 2005/6.

The GMB also took centre stage early last year when it held demonstrations outside some of the offices of 72 recruitment agencies which supplied staff to Asda.

• Recruitment agencies might face more problems from unions over the coming months: T&G delegates recently passed a motion to form the UK's largest union by merging with Amicus. Both unions represent staff from a wide variety of sectors. The new organisation will have some 2m members, giving it more muscle if it supports strikes or other industrial action.