Mr Yasin was elected as MP for Bedford in last year's snap General Election after winning the seat from the Conservatives.
It follows reports of threatening letters calling for a day of violence against Muslims on April 3.
A member of Huq's staff has been taken to hospital as a precaution after opening the letter, which the MP told the Guardian was a "sticky substance" and the police had described as "low-level noxious". "It is frightful 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".
Urging people to join their "day of action" next month the letter reads: "They have hurt you, they have made your loved ones suffer".
Bangladeshi-origin MPs Rushanara Ali and Rupa Huq and their Pakistani-origin colleagues Afzal Khan and Mohammad Yasin are the four Labour party MPs to receive the same kind of package in their parliamentary offices within the Palace of Westminster over the last two days.
"We are aware of a potential situation involving a suspicious substance which the Met Police are investigating", a parliamentary spokesperson said.
Scotland Yard announced that an anti-terrorism investigation was under way to identify the ones behind these letters.
At least three police officers and five paramedics were called to the scene inside Norman Shaw North amid reports of a leaking package.
The spokesman said there were no reported injuries and inquiries were continuing.
HuffPost UK understands a package containing an unknown liquid - which was later deemed non-hazardous - was sent to the office of the Bedford MP, but he did not personally open it.
A Commons spokesperson said: "Today a suspicious substance was investigated by the Met Police and was found not to be hazardous. A man and a woman have been taken to a central London hospital as a precaution", a statement said.