Hong Kong’s decision to query opposition candidates about ties with foreign governments suggests authorities could be preparing to use new national security legislation to disqualify pro-democracy advocates ahead of a key fall election.

At least seven potential pro-democracy candidates for Hong Kong’s Legislative Council elections have received questionnaires from the government asking them to show they haven’t violated the city’s miniconstitution, known as the Basic Law, or the recently imposed security measures.

The move fueled concerns within the pro-democracy movement that Hong Kong officials might use provisions of the security law — which bars subversion, secession, terrorism and foreign collusion — to question, undermine or disqualify opposition candidates who have previously criticized the local administration and the government in Beijing.