BOSTON (AP) – The Coast Guard is investigating an apparent near-collision in Boston Harbor in which a 600-foot carrier ship almost struck a pier at an Exxon terminal.

The ship narrowly missed the pier, which is near the liquefied natural gas terminal in Everett, after three tugboats nudged it back on course, said Lt. Edward Munoz, senior investigator for the Coast Guard in Boston.

The dock had no LNG ships at the pier at the time of the incident on Monday, Munoz said. He said the Coast Guard has opened up a preliminary investigation “as a routine.”

Munoz said investigators are looking into whether pilot error may have caused the ship, which was carrying rock salt, to come so close to the pier. There were no injuries.

The incident has prompted some lawmakers to call for tougher regulations to protect heavily populated city neighborhoods against catastrophic collisions in the harbor.

“This incident shows we need to make sure that the people controlling these vessels … have the right skill set to navigate Boston Harbor,” said state Sen. Bruce Tarr, R-Gloucester, who chairs a subcommittee crafting a series of proposed regulations.