Nicola Sturgeon and Ian Blackford have been among those calling on Ferrier to stand down.
The SNP leader says she hopes Ferrier "will do the right thing" after taking a train from Glasgow to London and back with coronavirus.
Nicola Sturgeon's party won 48 of Scotland's 59 seats, ousting seven Tories and Lib Dem leader Jo Swinson.
Motion of no-confidence and general election could follow in November if Commons blocks Queen's speech.
Westminster leaders could turn to judges if Boris Johnson asks the Queen to prorogue parliament.
Johnson has stoked division in communities and has a record of dishonesty – he's simply not fit for the office of prime minister, SNP MP Ian Blackford writes
Ian Blackford told to be "extremely careful" by Speaker John Bercow as he questions whether Johnson fit to be PM.
The meerkat is out of the bag.
Who knew it was that easy?
"The UK Government must stop running down the clock."