Labour frontbenchers have criticised the chief executives of HSBC and Standard Chartered banks for supporting China’s political leaders, urging them to revoke their support for Beijing’s controversial security law, which they say threatens democratic rights in Hong Kong. They warned the banks that they could face a boycott.

In letters sent to the HSBC boss Noel Quinn and Standard Chartered’s chief executive, Bill Winters, on Friday, the shadow foreign secretary, Lisa Nandy, and the shadow chancellor, Anneliese Dodds, said they had “profound concerns” that both banks had backed Beijing’s new rules, which violate Joint Declaration treaty commitments and could limit freedoms for HK citizens.

“As a senior figure in the banking industry, you will also understand the importance of maintaining the rule of law and the international rules-based order,” the letter said. “Quite apart from the morally abhorrent nature of the statement, we also find HSBC’s support for the autocratic actions of the Communist party of China to be completely at odds with the values framework in which financial institutions should be operating.”

The Labour MPs also wrote to their counterparts in Downing Street – the foreign secretary, Dominic Raab, and the chancellor, Rishi Sunak – asking for their support in challenging the two banks over their positions.

The letter said the ministers’ response would be a “test of the UK government’s resolve” on human rights, civil liberties and international law.

The Labour frontbenchers said the British public no longer trusted China to act responsibly, and warned that the banks risked boycotts similar to those aimed at South Africa over apartheid in the 1980s if they failed to uphold democratic values.

In their letter to HSBC’s boss, they said: “It would presumably not therefore come as a surprise if public attitudes were to harden against HSBC as a consequence of the decision to support the aggressive expansionism of the Chinese Communist party,” the letter added.

The letter stressed that, despite their global operations, both banks were still headquartered in London. “It therefore has a responsibility to uphold the democratic values and practices that we hold dear in this country – indeed HSBC’s 8 million British customers rightly expect nothing less. 

 “We therefore urge you to issue a statement rescinding HSBC’s support for China’s new national security law, at the earliest opportunity.” A similar letter was sent to Standard Chartered.

The Labour letters ramp up the political pressure on both banks, which faced a barrage of criticism on social media from both Tory and Labour politicians earlier this week over their support for Beijing’s new law.

They took issue with HSBC’s statement, which read: “We respect and support laws and regulations that will enable HK to recover and rebuild the economy and, at the same time, maintain the principle of ‘one country two systems’.”

Standard Chartered, meanwhile, has said it believed the national security law would help “maintain the long-term economic and social stability of Hong Kong”.

“The ‘one country, two systems’ principle is core to the future success of Hong Kong and has always been the bedrock of the business community’s confidence. We hope greater clarity on the final legislative provisions will enable Hong Kong to maintain economic and social stability.

“We remain positive that Hong Kong will continue playing a key role as an international financial hub and Standard Chartered is committed to contributing to its continued success.”

HSBC and Standard Chartered were both contacted for comments on Labour’s letter.