A group representing Moroccans living in the Netherlands says it will file a complaint of discrimination against the populist politician, Geert Wilders.
At a local election rally in The Hague on Wednesday night, Mr Wilders asked supporters of his Freedom Party if they wanted more or fewer Moroccans there.
When they chanted "fewer" in response, Mr Wilders said: "We'll organise that."
The Dutch Moroccan Alliance (SMN) said he had crossed a legal boundary by targeting a specific group of people.
Video footage of the rally is being circulated on social media with some critics drawing comparisons between Mr Wilders and Adolf Hitler's call for the "irrevocable removal" of Jews from German life.
They accuse the outspoken politician of alluding to a promise of action that, taken to its literal conclusion, could resemble ethnic cleansing.
SMN spokeswoman Mariam Elmaslouhi told the BBC that Mr Wilders' actions had been "outrageous".
"It's illegal," she told the BBC. "In the past he was always criticising only ideology or religion and of course everyone has a right to do this."
"But now he is attacking an entire ethnic group. Now he's gone a step too far it's very scary and potentially dangerous."
This is not the first time the controversial politician has targeted the Netherlands' significant Moroccan population.
In the past he has referred to a specific "Moroccan problem", blaming young Moroccan men for an increase in crime and anti-social behaviour.
Following Wednesday's rally, Mr Wilders said he had been "only referring to Moroccan criminals".
A representative from the Freedom Party (PVV), who wished to remain anonymous, told the BBC: "Immigration is a problem, criminals should have their passports withdrawn and no new Moroccans should be allowed into the country."
Mr Wilders' comments came as exit polls from local elections in The Hague revealed that the anti-Islam, anti-immigration PVV was running neck-and-neck with the liberal-leaning D66 party.
In the end, the PVV was narrowly nudged into second place in The Hague, winning 14.1% compared to 15.4% secured by D66.
But the result, and the enthusiastic response to his anti-Moroccan rhetoric, will galvanise Mr Wilders ahead of the European Parliament elections in May.
He has consistently campaigned on an anti-EU ticket, blaming "the monster in Brussels" for stealing Dutch politicians' ability to make decisions about how the country should be run.
The PVV is the fourth largest party in the Dutch parliament but leads most national opinion polls.
Mr Wilders' popularity has rocketed over the last 10 years, after the murder of anti-Islam politician Pim Fortuyn spurred a surge of anti-immigrant sentiment in a country once famous for its liberal and tolerant attitudes.
In 2011, Mr Wilders was acquitted of incitement after being accused of encouraging hatred towards Muslims.