LONDON — The British police are investigating threatening packages received this week by Muslim members of Parliament that contained a letter calling for “Punish a Muslim Day” and, in some cases, a noxious substance.

Sajid Javid, the secretary for housing, communities and local government in Prime Minister Theresa May’s cabinet, was among those who received the letter. Mr. Javid posted on Twitter a photo of the letter sent to him on Thursday.

It said that people would be awarded points for harming Muslims on April 3 for a series of offenses — from verbally abusing them to burning or bombing a mosque to nuking Mecca.