"MPs have lined up a legal team and are willing to go to court to enforce the law to avoid no deal, if necessary," the message reads.
The legislation demanding from Boris Johnson to seek a delay of the British exit from the EU to avoid a no-deal Brexit should be approved by the Queen.
The PM said he would be prepared to leave the EU without a deal, but Labour party representatives say stopping a no-deal Brexit is their priority.
Legal experts warned that the Prime Minister could go to prison if he refuses to uphold the new law.
Meanwhile, pro and anti-Brexit protesters held demonstrations in Westminster on Saturday, with some people arrested by police.