They've been doing this passively for the last two years, if they randomly checked a container it was siezed and if a local port came to associate your name with imported engines then everything you brought in was inspected.
A local importer started importing whole cars to Mexico and driving them across the border. Only to find out they can't get them titled like they used to. I spoke with a local dude who tried to get a RHD JZA80 from them but the kit car application he filed was denied (duh).
Who cares? I like USDM engines anyway, and I prefer to rebuild anything that's 10+ years old and mostly worn out.