A Hong Kong court on Thursday sentenced the younger sister of a pro-democracy labour union leader to six months imprisonment for removing evidence from the latter’s home amid an ongoing security crackdown in the China-ruled city.

Marilyn Tang, 63, had earlier pleaded guilty to perverting the court of justice after she removed devices including a laptop and mobile phone belonging to her sister, Elizabeth Tang, soon after she was arrested in March.

Magistrate Patrick Tsang said while the offence wasn’t very serious and that the defendant hadn’t “turned on or obstructed the devices” he still handed down a custodial sentence.

Elizabeth, 65, had been arrested on March 9 for collusion with foreign forces under a China-imposed national security law, soon after she returned to the city to visit her jailed pro-democracy activist husband Lee Cheuk-yan, 66.

The husband, a former lawmaker and leading democrat, faces an incitement to subversion charge under the national security law and is awaiting trial.

The two sisters had been linked to the Hong Kong Confederation of Trade Unions (HKCTU) – the city’s largest opposition trade union coalition that disbanded in 2021 after several members received messages threatening their safety. Elizabeth had served as its chief executive.

Tang’s lawyer Robert Pang had earlier told the court during a mitigation hearing that Marilyn’s behaviour was “not premeditated” while highlighting her lifelong service to the community.

Pang added that Elizabeth’s laptop and phone only contained personal information, family pictures and letters to her husband which had no direct impact on the police investigation.

More than 280 people have been arrested so far in Hong Kong under the national security law that punishes acts including subversion, secession, collusion with foreign forces, and terrorism with up to life in prison.

Leading China critic and media tycoon Jimmy Lai, 76, is currently battling a foreign collusion charge in a closely watched trial that has become a diplomatic flashpoint.

The national security law has been criticised by some Western governments as a tool to curb free speech and dissent while the Hong Kong and Chinese governments say it has restored stability after mass, pro-democracy protests in 2019.