Dozens of pitches and client meetings have been postponed in the aftermath of the disaster, which destroyed the twin towers of The World Trade Center in New York.
PR agency Ketchum -- which boasts a large American contingent among its board of directors -- is one of the firms affected.
Ketchum marketing and new business director Anna Burns confirmed one US firm had put its search for an agency back a week as chaos reigned and added that Ketchum bosses declined an offer from one potential client to postpone a pitch meeting.
Weber Shandwick Worldwide joint UK CEO David Brain also confirmed one major travel client had already alerted the agency
that it would be reviewing budgets due to the financial impact of the disaster.
He added that many expected decisions on major accounts and client meetings had been postponed, in part due to the travel upheaval that ensued.
Another senior industry figure said credential meetings -- scheduled by a UK insurance company -- had also been cancelled.
The situation was compounded by precautions imposed by a number of client companies.
A Procter & Gamble spokesman confirmed the FMCG giant had imposed a week-long ban on staff travelling by air after the tragedy.
PRCA chairman Dr Tom Watson said: 'It is not surprising that clients may choose
to focus their attention elsewhere as they struggle to come to terms with the implications of this disaster.'
But Brain sounded a more positive note for the industry amid fears of global recession.
'Obviously firms affected, such as the airlines, need crisis and issues help, but for clients not directly involved in the tragedy, PR firms are well placed to advise on and interpret what this means for their businesses in the long-term.'