The Canada Border Services Agency (CBSA) is reporting six separate seizure incidents between March 5 and 11 at the Ambassador Bridge.
Over this period, the CBSA says its officers at seized four firearms, a number of restricted and prohibited magazines, and a prohibited knife.
All travellers involved were U.S. citizens who were arrested under the Customs Act; each paying a varying fine between $500 and $2,000.
The CBSA said each traveller was returned to the U.S.