The letters also put down countries with migrant, minority and Muslim populations.
Speaking in the House of Commons after hearing news of the incident, Tory MP Michael Fabricant raised fears the package sent to Mr Yasin may be connected to reports anti-Muslim letters have been posted across the country.
"The letter calling for attacks on Muslim is just the latest example of rising Islamaphobia and deplorable hate crimes in this country", said Pakistani-origin Labour MP Yasmin Qureshi, who raised an urgent question in the House of Commons yesterday calling on the United Kingdom government to do more to tackle such "incitement to violence and help prevent the growth of such extreme views".
Four Muslim Labour MPs have been sent suspicious packages over the last 48 hours, at least three of which included copies of a "Punish a Muslim" letter that advocated violent acts against Muslims.
AFP also reports that the package was delivered to the office of the Muslim Labor MP Mohammad Yasin, who was not there at the moment.
A second suspicious packaged in as many days has been found at Westminster, with one person hospitalised as a result. "Someone out there thinks it is open season on Muslims", said Huq, who represents Ealing central and Acton in south-west London. "It is terrible though, it's really very frightening", she told the Guardian.
"Tell MAMA documented past year how the so-called "Muslim Slayer" targeted mosques in parts of London and the United States in 2017 with similar threats, and in some cases, with non-toxic white powder".
The people behind this initiative have not been identified yet, but their letters are distinguished by a hateful speech: "They have hurt you".
Emergency services were called to Norman Shaw North, a Parliamentary building, just before 1pm on Monday. "This is further to the two items investigated yesterday, both of which were found to be non-harmful". It released a statement, saying: "It is essential that all letters and envelopes are kept and handled minimally to preserve evidence for the police to investigate. Two people attended hospital as a precaution".
The substance has since been found to be non-hazardous, according to police.
The spokesman said there were no reported injuries and inquiries were continuing. "The incident, which was contained to one room, has been stood down".