Persian Gulf Strait Authority said it would take “legal action” against tankers belonging to Sinokor, the world’s biggest oil tanker owner that has carried millions of barrels out of the Strait of Hormuz in recent weeks.

“The vessels belonging to Sinokor Shipping Company have committed the highest number of crossing violations over the past 3 months, and so far, appropriate enforcement actions have been taken against at least 7 of them,” the PGSA said in a social media post, without specifying what those actions were.

Iran established the PGSA earlier this year as a point of contact for transits through Hormuz. It has since published a list of vessels that it says have violated its rules for crossing the waterway.

Meanwhile Sinokor is the world’s largest owner of supertankers and has emerged as a vital cog in keeping the world’s oil moving, by pouncing on the lucrative trade of getting barrels out of Hormuz. The company’s ships accounted for nearly 40% of all the crude oil that flowed out from the Strait of Hormuz last month, more than the next three biggest players combined, according to data from intelligence firms and maritime databases.

Since the Iran war began, there’s been a tussle for control of the world’s most important energy chokepoint. While it was largely shut in the immediate aftermath of the conflict, there’s been a persistent increase in the amount of oil transiting Hormuz since, and most trackers now see total shipments from the Middle East around pre-war levels.

“All cargo owners, stakeholders, and insurance service providers are hereby warned that as of November 1, legal action will be taken against all vessels of this company,” the PGSA said in its post. Sinokor didn’t immediately respond to a request for comment.