Thompsons Solicitors, which has been working with the public health charity ASH in its campaign against secondhand smoke, has made the unprecedented call through its staff newsletter.

Thompsons' Christmas message to its nearly 1,000 staff says that the government's white paper on proposing a ban on smoking in the majority of workplaces by 2008 does not go far enough.

Pubs and clubs not serving prepared foods, along with private clubs, will be exempted from the ban. Thompsons says it will be impossible to set safe standards for them and that the fight for the right of workers not to be exposed to second-hand smoke continues.

John Hall, the solicitor advising ASH, said: "This is a fundamental issue for us, both as an employer and as a campaigning firm. Anything we can do to encourage awareness of second hand smoke as a health and safety at work issue is important to us."

Thompsons, which is the largest trade union law firm in the country, has fought a number of test cases on workplace health and safety, including for the right of workers exposed to asbestos to claim compensation.

ASH and Thompsons wrote to the UK's leading hospitality trade employers earlier this year, warning them that the "date of guilty knowledge", under the Health and Safety at Work Act, is past and that employers who continue to permit smoking in the workplace are therefore likely to be held liable by the courts for any damage to health. A number of pub chains have since said they are considering a voluntary ban on smoking.

The firm says the next stage in the campaign on secondhand smoke may be action under the Human Rights Act.