Britain's postal workers may strike next month if the government does not provide guarantees on pay and pensions before privatising the near 500-year-old Royal Mail, Reuters reports.

The Communication Workers Union (CWU), which represents most of the Royal Mail's 150,000 staff and which rejected Royal Mail's three-year pay offer in July, said it would send out strike ballot papers on 20 September if it could not reach an agreement on talks.

"We are looking to reach a groundbreaking agreement on terms and conditions that sets unprecedented legally binding protection for workers in the event of a sale, and regardless of who owns the company," deputy general secretary Dave Ward said.

The CWU said if the ballot went ahead it would publish the result on October 3. If workers were in favour, the earliest date for strike action would be October 10, Reuters said.

Any industrial action could complicate the privatisation process. The government plans to float a majority stake this financial year.

Royal Mail said in a statement it was committed to talks with the CWU and wanted to reach an agreement as soon as possible. "We believe a strike is uncalled for, given the highly competitive three year pay offer and legally-binding and enforceable agreement we have offered CWU," it said.