Elon Musk’s companies SpaceX and Tesla are to join the ranks of technology firms officially opposing the migrant ban imposed by the US president, Donald Trump, standing alongside the 97 firms who signed up to an amicus brief on Sunday night.

The companies are supporting a lawsuit brought by Washington state against the ban, which affects millions of people from seven majority-Muslim nations. The suit, which is currently being heard in the ninth circuit federal court in San Francisco, California, has already succeeded in imposing a temporary halt to the enforcement of Trump’s executive order.

While SpaceX and Tesla were not signatories of the original version of the amicus brief, a Tesla spokesperson told the Verge that “as soon as we saw the brief this morning, we insisted on being added”. Previously, Musk had argued that he would use his membership of Donald Trump’s advisory forum to “express our objections to the recent executive order on immigration”.

Along with Tesla and SpaceX, 29 other companies also joined the brief, including Adobe, HP, Bungie and Slack. Separately, companies including Groupon and Pivotal software have filed their own letters supporting the amicus brief.

Another amicus brief, supporting the migrant ban, was filed by a collection of rightwing organisations, including the English First Foundation, Gun Owners of America, Citizens United and the Conservative Legal Defence and Education Fund.