Two of the main witnesses in the US government's case against Russian software company ElcomSoft have been denied US visas – despite the trail beginning next week.

The US Embassy in Moscow has denied visa applications for ElcomSoft employee Dmitry Sklyarov and company chief executive officer Alex Katalov.

ElcomSoft immigration attorney Marina Serebryanaya said: "We are working with the State Department and the Department of Justice on this issue. Obviously, not having Dmitry and Alex here in the US is a problem for both sides.”

The visa hitch is expected to delay the October 21 trial, which will represent the first time criminal charges are taken to trial under the Digital Millennium Copyright Act (DMCA). Moscow-based ElcomSoft is being charged under the Act for developing and distributing a software program that allows users to circumvent copyright protections in Adobe's eBook file format.

Sklyarov and his employer were indicted last year after the programmer gave a presentation on the software at the Def Con hacker conference in Las Vegas. Sklyarov was briefly sent to jail but released amid a public backlash. Criminal charges against him were later dropped in exchange for his agreement to cooperate in the case.

The trial is due to take place in the US District Court for the Northern District of California, in San Jose.