Beverweerd Investments, a Dutch company linked to BCD Travel, has increased its stake in UK rivals Hogg Robinson Group (HRG) to 13.14%.
It is Beverweerd's third foray into HRG shares in the last five months.
It initially declared a 4.3% stake in the travel management company just before last Christmas.
The stake was increased to 10.1% in March but at the time, a spokesman for Beverweerd said it was simply "a long-term investment and not a preparation for a takeover bid."
After it latest purchase Beverweerd now owns 40,155 million shares in the company.
Beverweerd is a private investment vehicle of the John Fentener van Vlissingen family which in turn owns BCD Holdings, the parent company of BCD Travel.
BCD, like HRG, is among the biggest travel management companies in the world.
The two companies previously worked together in a joint global enterprise called BTI. This broke up in January 2006 when both companies decided to go their separate ways.
HRG floated on the London Stock Exchange in 2007 but its shares have fallen sharply this year after the company issued a profits warning in March.
The shares dropped from 58p at the end of February to 41p when the profits warning was issued in mid-March.
They have since continued to drop slightly and reached a year low of 33p last week before rising again to 35p. After the news of Beverweerd's increased stake, they rallied to close last night (April 30) at 39.50p.