The increasingly litigious Pitney Bowes Inc got a taste of its own medicine Friday when, as it had filed its second patent infringement lawsuit in a week, this time against Stamps.com Inc, it was revealed that the US Department of Justice contacted the Stamford, Connecticut firm two days earlier to let it know that it was starting an investigation into Pitney for possible antitrust violations. Pitney believes it is in full compliance with all antitrust legislation.

Seven days earlier, Pitney had filed a similar suit against E-Stamp Inc, the other company with US Postal Service (USPS) approval to test its internet-based postage system. Pitney says it has tried negotiating with both companies, but no agreement had been reached – hence the law suits. It says it is also in talks with Neopost about similar matters.

In August last year, Pitney fired a shot across the bows of E-Stamp and Stamps.com by warning them that it had a bunch of patents dating back to the 1970s concerning the delivery of postage to computers, which was widely, and it turns out, correctly seen as an indication that it intended to pursue any possible infringements of those patents. Pitney is behind the other two companies in terms of developing its technology, as they are both in the final phase of testing their internet postage technologies, while Pitney only got approval from the USPS just last November for its ClickStamp system.

It has two versions, ClickStamp Plus which uses a separate piece of hardware to store the postage value, like E-Stamp’s system and ClickStamp Online, which is a pure web play, like Stamps.com. ClickStamp Plus is on phase two of the three-phase beta test managed by the USPS and Online is on the first phase. E-Stamp and Stamps.com are both on phase three and are expected to roll out their services nationwide in late summer.

Pitney is obviously looking for these companies to license its technology, which would most likely settle the suits. It says all its competitors in the postage meter business license its patented technology in that area and the practice is commonplace in the postal industry, it says.