A broad coalition of US technology firms has begun planning a joint legal strategy challenging President Donald Trump's executive order barring refugees and many Muslims from American soil, sources say.

More than 20 firms from the sector were expected to attend a meeting to discuss legal options on the ban, which was expected to have a large impact on Silicon Valley and other tech firms which employ thousands of immigrants.

"It's still very early, but the strategy would probably be similar to the San Bernardino iPhone briefs," said one tech sector employee familiar with talks on condition of anonymity.

The source was referring to the coalition which fought a US government order which would have forced Apple to weaken iPhone security to inspect a handset used by one of the shooters in a deadly attack in Southern California in December 2015.

Participating in the talks were Google parent Alphabet, Netflix, Airbnb and Twitter, the source indicated.

RELATED: Sudanese Scientist Blocked from U.S. Travel Considers Handing Over Prestigious Award

Other firms invited or participating include Adobe Systems, Dropbox, Etsy, Mozilla, Pinterest, Reddit, Salesforce, Yelp, SpaceX and Zynga, according to the source.

The talks included "several" member companies of a Washington-based technology policy association, according to a separate source.

Trump's order has provoked widespread outrage, including from technology firms, with executives from Google, Microsoft, Facebook, Apple and Netflix expressing concerns over the ban.

The executive order, signed Friday, suspends the arrival of refugees for at least 120 days, and for the next three months bars visas for travelers from seven Muslim-majority countries: Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen.

WATCH: How Powerful Is Twitter?