The Home Secretary came under fire in the Commons after almost 1,200 people reached the UK in small boats on Saturday - the first four-figure daily tally this year.
The Home Secretary said those found to be illegally employing migrants who are blocked from working face up to five years in prison, huge fines or have their firms closed down.
Yvette Cooper said it was 'hard to see how an inquiry would be able to go beyond' terrorist killer Ali Harbi Ali's trial and the recently published Prevent learning review.