The new Strikes (Minimum Service Levels) Bill gives the Government the power to ensure unions provide essential cover
The union said its members in 124 government departments and other bodies will walk out on February 1.
Teachers and some secondary school pupils protested outside Nicola Sturgeon’s official residence in Edinburgh on Wednesday.
The company’s comments come after MPs debated the future of postal services.
Lawyers from several UK firms have said that employers are unlikely to want to sack their workers over breach of the proposed law.
NHS England has told patients to continue to call 999 for life-threatening emergencies but to use 111, GPs and pharmacies for non-urgent needs.
Hundreds of students will not be in school as the teaching strike continues today.
Paramedics, emergency care assistants, call handlers and other staff will stage a major walkout on Wednesday.
Thousands of members of the Transport Salaried Staffs’ Association in Network Rail will strike.
The number of people supporting calls for a general election has increased since Liz Truss resigned as Prime Minister.