The United Auto Workers (UAW) has summoned local union leaders to Detroit on Thursday for an update on its negotiations with General Motors.

This came as the strike entered its fifth week.

CNBC noted the union has traditionally done this when a tentative agreement has been reached or, as was the case a month ago, to discuss and vote on other actions such as a strike.

A letter to local union leaders on Monday night, cited by CNBC, said the agenda for the meeting included a "contract update and any other agenda items to be determined", leaving the door open for talks to continue to potentially reach a tentative agreement ahead of the meeting.

UAW spokesman Brian Rothenberg declined to comment to CNBC on the letter. GM spokesman David Barnas confirmed to CNBC talks were "ongoing", but declined to comment on details of the discussions. Negotiations between the two sides ended on Monday evening and were expected to resume Tuesday morning.

If a tentative agreement is not reached by the meeting at 10:30 am Thursday, the union could update local leaders about the discussions in an attempt to determine what to do next, CNBC said.

"My guess is if there is no tentative agreement by Thursday, they will review the status of bargaining with the council and then try to obtain a consensus with respect to next steps," Colin Lightbody, a labour consultant and longtime negotiator for Fiat Chrysler, told CNBC.

Options for the union moving forward could include remaining on strike and continuing negotiations with GM, discussing and voting on terms for remaining outstanding issues, moving discussions to another automaker if negotiations have stalled, among others, CNBC said.

Wall Street analysts have estimated GM has lost over US$1bn due to the strike.