This is one of the most common worries people have once they understand how matched betting actually works, and it deserves a straight answer instead of a reassuring dodge.
The direct answer
A sportsbook can restrict, limit, or close your account, and doing so is not illegal or a violation of anything on your part, because sportsbooks are private businesses that can manage their own promotional spend however they choose. This is a business decision they are allowed to make, not a penalty for wrongdoing, and it carries no legal consequence for you at all.