The Muslim Council of Britain has formally asked the UK's human rights watchdog to investigate accusations of Islamophobia in the Conservative Party.
In a letter to the Equalities and Human Rights Commission, the MCB said a problem "runs deep into the party".
The EHRC said in response that it was considering complaints about the party in line with its "usual processes".
In March, party deputy chairman James Cleverly insisted "immediate action" was taken after any racism claims.
The MCB is an umbrella organisation of various UK Muslim bodies, including mosques, schools, and charitable associations. It has called repeatedly for an independent investigation into discrimination claims.
Now, in its letter filing a formal complaint to the EHRC, it accused the Conservatives of not taking action against Islamophobia shown by Tory MPs, and tolerating discrimination towards party members.
The MCB said there was "sufficient evidence" to suggest the party may have breached anti-discrimination law, and accused it of showing a "callous attitude to complaints".
Among the allegations, it cited comments made by Boris Johnson about women wearing burkas looking like "letter boxes" or "bank robbers" as an example of when Tory MPs had created an "atmosphere of hostility towards the Muslim members of the party".
The former foreign secretary was later cleared of breaking the Tories' code of conduct - a decision the MCB criticised at the time.
The group also criticised the unsuccessful London mayoral campaign of Zac Goldsmith in 2016 - in which he ran against Sadiq Khan - arguing it demonstrated a "tolerance for Islamophobia" within the Conservative Party.
The MCB complaint comes on the same day that the EHRC announced a formal investigation into the Labour Party over allegations of anti-Semitism.
Conservative peer Baroness Warsi, who was the first female Muslim cabinet minister, has long criticised her party over the issue.
In April, Tory chairman Brandon Lewis insisted the party's approach to Islamophobia was "transparent" but would not say how many complaints it had received.
An EHRC spokesman said the body had written to the Conservative Party "to ask for information in order to help assess the complaints".
Earlier this month, the MCB criticised the government for rejecting a definition of Islamophobia created by a cross-party group of MPs.
The All-Party Parliamentary Group on British Muslims wanted to define it to tackle what it called a "social evil".
Its wording has the support of various political parties - including Labour, the Liberal Democrats and the Scottish Conservatives - and several Muslim groups.
But a government spokesman said it needed "further careful consideration" and had "not been broadly accepted".