First it was General Motors, now it's apparently Chrysler's turn.

The United Auto Workers union (UAW) has put Chrysler on notice that a strike is possible if contract talks stall, a person briefed on the talks told the Associated Press (AP), but a labour expert reportedly said the union's action could be a bargaining tactic.

The union on Sunday gave Chrysler a 72-hour notice of a potential strike, the person told AP, but it was unclear exactly whether the notice would end on Tuesday or Wednesday. The New York Times said it had been told the deadline was Wednesday.

AP's source said bargainers working in committees made progress during the weekend but still have much work to do on difficult issues.

"We remain optimistic," Chrysler spokeswoman Michele Tinson told the news agency on Sunday afternoon while UAW spokesman Roger Kerson declined to comment on the talks.

Harley Shaiken, a professor at the University of California at Berkeley who specialises in labour issues, told the Associated Press that a strike notice could be a tactic by the union to put pressure on the company as the talks intensify.

"The union wants the deadline to encourage a settlement sooner rather than later," Shaiken reportedly said.

The UAW went on strike for nearly two days last month before coming to a tentative agreement with General Motors whose UAW union member workers are now voting on the settlement branch (local) by branch.

AP noted that the union normally settles with one US automaker and then uses that deal as a pattern for an agreement the other two but, this year, both Chrysler and Ford have said they have different needs than GM and may need different contract terms.

The union has not formally picked the second company it will negotiate with, but talks with Chrysler have intensified in recent days, AP noted.

Shaiken told the news agency the notice doesn't necessarily mean there will be a strike because the UAW could extend its contract hour-by-hour when the deadline passes. A second strike in one set of negotiations would be rare, he said.

"I think the union may feel things are going well, but they want the discipline of a deadline," Shaiken told the Associated Press.

Chrysler temporarily shutting factories