By Doyinsola Oladipo and David Shepardson

NEW YORK/WASHINGTON (Reuters) - A strike by 45,000 dockworkers halting shipments at U.S. East Coast and Gulf Coast ports entered its second day on Wednesday with no negotiations currently scheduled between the two sides, sources told Reuters.

The lack of progress is raising concerns among those reliant on shipments that the disruption could be prolonged.

The International Longshoremen's Association union strike has blocked goods from food to automobile shipments across dozens of ports from Maine to Texas, which analysts warn will cost the economy billions of dollars a day.

President Joe Biden’s administration has put pressure on U.S. port employers to raise their offer to secure a deal with dockworkers to end the strike.

"They made incredible profits, over 800% profit since the pandemic, and the owners are making tens of millions of dollars from this," Biden told reporters on Wednesday. "It's time for them to sit at the table and get this strike done."

Economists have said the strike will not initially raise consumer prices as companies accelerated shipments in recent months for key goods. However, a prolonged stoppage will eventually filter through, with food prices likely to react first, according to Morgan Stanley economists.

Packaged food maker Conagra bought ingredients ahead of time and has been working with suppliers for months to prepare for the strike, CEO Sean Connolly said on Wednesday. "If it becomes a protracted issue, it will be a bigger issue for everybody," he said.

More than 38 container vessels were backed up at U.S. ports by Tuesday, compared with just three on Sunday before the strike, according to Everstream Analytics.

Crock-Pot maker Newell Brands has hundreds of containers filled with items manufactured in Asia arriving at West Coast ports this week after being re-routed from the East Coast 2-3 months ago.

The company said that there is a "little bit of a backup" at West Coast ports but that they're still operating at full capacity.

The ILA, which represents 45,000 port workers, launched its strike on Tuesday after negotiations collapsed with the United States Maritime Alliance (USMX) for a new six-year contract. The union is seeking a $5-per-hour wage hike each year over six years.

Its leader Harold Daggett is also seeking an end to automation projects that he says threaten union jobs.

"We are prepared to fight as long as necessary, to stay out on strike for whatever period of time it takes, to get the wages and protections against automation our ILA members deserve," Daggett said on Tuesday.