Rail track maintenance means restricted services into the Welsh capital on Sunday, May 3 and fans are asked to check train schedules carefully.
Toms, the man in charge of the Welsh national stadium, says contingency arrangements are in place to cope with the flow of fans expected from the Midlands and throughout the country.
The Blues set a Heineken Cup record for a home attendance in Wales for their quarter-final meeting with Toulouse when more than 36,000 fans saw them seal a 9-6 victory.
Tigers supporters are also used to filling the Millennium Stadium, venue for victory in the 2002 Heineken Cup Final in front of a capacity crowd of 74,600. Attendance at the semi-final is expected to be high.
“The rail maintenance shouldn't be a major problem for spectators provided we can get the message out far and wide that they will need to plan their journeys in advance and preferably travel in groups," said Toms.
"Free parking will be available at the Civic Centre at Cathays Park for coaches and minibuses which is the advised way to travel. There will also be an extensive park-and-ride facility in Cardiff Bay signposted from the main arterial link into Cardiff, the M4.
"The rail maintenance had been planned well in advance of the fixture being scheduled and, while it is unfortunate timing, the Millennium Stadium and Cardiff city are well used to ensuring travel conditions for major events are of the highest standards possible.
“The important thing is that fans are aware of the issue and can now plan to work around it by using coaches, minibuses or car sharing wherever possible."
Coach or minibus travelers can use free parking at the Civic Centre at Cathays Park. Coaches should follow M4 electronic signs and exit at junction 32, follow A470 south to City Centre.
Those travelling by car should follow M4 electronic signs to junction 33 and follow signs south along A4232 to park-and-ride facilities in Cardiff Bay. The park-and-ride will operate 10am-7pm and will cost £5 per car.
Supporters are strongly advised to check with the rail authorities before selecting train travel.
The Tigers Travel Club will be running coaches to Cardiff, price £18 for season ticket holders and members, and £21 for non-members. Coaches will depart Welford Road at 8.30am and leave the Millennium Stadium an hour after the final whistle.
Contact the Tigers ticket office on 0844 856 1880 or call in at Welford Road. The ticket office is open as normal during the redevelopment work on the new Caterpillar Stand, 8.30am-5pm Monday-Friday.