The Communication Workers Union has launched a campaign against what it claims are threats to working conditions and services at Royal Mail from privatisation and regulatory intervention.

The union said its “People’s Post” campaign was a response to the government’s declared intention to sell its remaining stake in Royal Mail and the regulator Ofcom’s demands for efficiency measures.

If Royal Mail succumbed to pressure and tried to change workers’ terms and conditions then the CWU could resort to industrial action.

The last government sold 70% of Royal Mail to investors in 2013. Following the sale of another 15% last month, Chancellor George Osborne announced in the budget on Wednesday that he intended to sell the remainder by April next year.

Ofcom’s comments about flexibility in workforces at other European postal companies and the regulator’s call for greater efficiency at Royal Mail show the regulator has working conditions in its sights, the CWU added. Both risk undermining working conditions and ultimately the universal postal service that delivers to all parts of the country for the same price, the CWU said.

At a rally to launch the campaign on Friday, Dave Ward, the CWU general secretary, said: “There are a lot of pressures coming on from competition, regulation and privatisation and it is pushing Royal Mail towards a race to the bottom.

In terms of what the postal worker does and the service they provide it’s still the people’s post Dave Ward, CWU general secretary

“This is a defiant message. The coalition may have been successful in privatising 70% of the company and this government may have been successful in selling, overnight without any public scrutiny, half the remaining stake, but in terms of what the postal worker does and the service they provide it’s still the people’s post.”

Royal Mail and the CWU reached a five-year agreement in 2013 designed to end many years of industrial strife. The union said it would not accept attempts to change the agreed terms.

Ward said the agreement was a groundbreaking deal that was working well but that it was not set in stone. There will inevitably be greater pressure on Royal Mail management and if the agreement comes under strain the CWU will fight back, he said.

“We are not frightened of industrial action. We’ve probably had more industrial disputes in the last 10 or 12 years than any other union. We want Royal Mail to be successful and I know Royal Mail faces some really big challenges.”

Ofcom has overstepped its remit and there should be an overhaul of regulation, the CWU argued. Promoting competition and cost cuts threatens Royal Mail’s daily deliveries and rivals should be banned from “cherry picking” in the letters market, the union said.

Ward argued that Ofcom had appointed itself as an arbiter of efficiency at Royal Mail when its job is to preserve the universal service.

Ofcom said: “Ofcom’s duty is to secure a universal postal service that is financially sustainable and efficient. If this is ever under threat, we have powers to step in, but questions of pay and contract terms are for the companies themselves.”

The decision in May of rival Whistl to stop delivering letters despite choosing the most profitable parts of the country and paying low wages showed Royal Mail was not wasteful, Ward said.

He wants the CWU to recruit members at other postal companies to fight for better conditions. Royal Mail should be the industry’s standard bearer for good pay and terms instead of being put under pressure to copy other companies whose workers are on insecure contracts with low pay, he added.

Ward said the CWU was against the sale of the government’s remaining stake but that the union’s campaign was designed to last beyond full privatisation. Town hall meetings with prominent speakers will be open to the public and members will be galvanised by the union concentrating on its main job of working for them, he said.